Gemara

(Abaye): If one gets Hana'ah [from Isurei Hana'ah] against his will, it is permitted;

(Rava): It is forbidden.

Version #1: If one intends to benefit, whether or not he could avoid benefit, all forbid;

If he could not avoid benefit, and does not intend to benefit, all permit.

They argue about when he could avoid benefit, and does not intend to benefit;

Both agree that R. Yehudah, who forbids Davar she'Eino Miskaven, forbids. They argue according to R. Shimon;

Abaye permits, like R. Shimon [holds that intent matters];

Rava says, R. Shimon permits only when he cannot avoid benefit.

Version #2: [Abaye and Rava agree that] R. Yehudah and R. Shimon argue about one who could avoid benefit, and does not intend to benefit;

If he could not avoid benefit, and does not intend to benefit, both Tana'im permit;

[Abaye and Rava] argue about one who cannot avoid benefit, and intends to benefit;

Both hold that R. Shimon, who says that it depends on intent, forbids. They argue according to R. Yehudah, who ignores intent. If he could avoid it, it is forbidden;

[When he cannot avoid benefit,] Abaye permits, like R. Yehudah [ignores intent of one who could avoid benefit];

Rava says that R. Yehudah ignores intent to be stringent when one could avoid benefit. He does not ignore it to be lenient when one cannot avoid benefit.

Berachos 53a: Rav Huna holds that we bless on fragrances only if they were made to be smelled.

Question (Beraisa): If one enters a fragrance store and smells fragrances, even if he was there the entire day, he blesses only once;

If he left and returned repeatedly, he blesses every time.

The fragrances are not meant to be smelled, yet one blesses on them!

Answer: Indeed, the owner wants people to smell them, to encourage them to buy them.

Rishonim

Rif and Rosh (43b and 9:13 DH Al): In the Yerushalmi, Rav Chisda says that it suffices to bless on lightning once a day. R. Yosi says that if the clouds scattered, he blesses each time. A Beraisa supports him. If one enters a fragrance store and smells fragrances, even if he was there the entire day, he blesses only once. If he enters and leaves, he blesses every time [he enters].

Rambam (Hilchos Berachos 9:3): On oil scented [with many spices,] like Shemen ha'Mishchah, one blesses Borei Minei Besamim.

Gra (OC 216:6 DH Shemen): The Rambam holds that this is Kesharta (of Berachos 43a). Our text says that one blesses Borei Atzei Besamim [if only fragrant wood was used].

Poskim

Shulchan Aruch (OC 217:1): One who enters a fragrance store with many fragrances, blesses Borei Minei Besamim.

Magen Avraham (1): The owner wants people to smell them and buy them. Therefore, one does not bless on fragrances in a room that is not a store, even if he intends to smell them, for they were not put there to be smelled.

Mishnah Berurah (1): Fragrances in the seller's room, and not in the store where many come, are not there to be smelled, so even one who enters in order to smell does not bless, unless he took them in his hand to smell. Taking them makes them like fragrances made to be smelled.

Mishnah Berurah (2): Some say that this is only if he intends to smell. Many disagree; even if he does not intend to smell, since they are made to smell, and he benefits, he blesses.

Kaf ha'Chayim (1): Therefore, one who enters an orchard does not bless even if he intends to benefit. It is better to take a fragrance in his hand and bless on it, lest he benefit from this world without a Berachah.

Bi'ur Halachah (DH ha'Nichnas): Eliyahu Rabah says that the same applies to a pharmacy. Misgeres ha'Shulchan (on Kitzur Shulchan Aruch) was astounded. A healthy person will not buy medicine, and sick people will buy it in any case [even if he does not smell it in the store]. The seller does not care whether people smell them! I say that perhaps he wants the smell to exude, so people will know that there is a pharmacy here! However, I am unsure for another reason (see Bi'ur Halachah below). Also, we can add the Taz' opinion that one who does not intend to smell does not bless.

Bi'ur Halachah (DH Ela): (Sa'if 3 says that we do not bless on scented garments, for the smell has no source.) If so, we bless in a store only if the fragrances are revealed, but not if they are in closed flasks, and the store becomes scented from each time they are opened. The Ro'oh says not to bless on incense that was consumed in fire. There I disagree, for the coals of the incense are intact. Here, one does not bless.

Gra (DH Mevarech): This is like Kesharta, according to the Rambam.

Mishnah Berurah (3): He blesses Borei Minei Besamim because there are Atzei Besamim and Isvei Besamim. This is unlike 216:10. There, he takes each by itself, so he blesses on each by itself. Here, he smells all of them together, so he makes one collective Berachah.

Shulchan Aruch (ibid.): If he sat there the entire day, he blesses only once.

Mishnah Berurah (4): It does not matter whether or not he diverted his mind, since the smell comes constantly. The seller blesses only once even if he enters and leaves, for he intends to return to his store. Some Acharonim exempt even the first time he enters his store. Therefore, it is good to intend to smell. Then, all agree that he blesses the first time.

Aruch ha'Shulchan (1): The Taz is correct. One blesses only if he intended. We permit when it is impossible and he does not intend, and all the more so [we are lenient] regarding Berachos!

Shulchan Aruch (ibid.): If he enters and leaves repeatedly, he blesses every time.

Mishnah Berurah (5): Surely, if he goes to another fragrance store, he must bless there.

Kaf ha'Chayim (6): This is even if he intended for the other store from the beginning.

Shulchan Aruch (ibid.): This is if he did not intend to return.

Taz (1): The Gemara connotes that one blesses only if he entered and intended to smell. If the smell comes automatically, he need not bless. This is like something not made to smell. This is why we did not teach that the seller does not bless each time he engages with them. Surely he is exempt, for he does not intend to smell.

Gra (DH v'Davka): This is like thunder and lightning. Even though each time it is a new bolt, since he did not divert his mind [he does not bless again]. The Yerushalmi compares these.

Mishnah Berurah (6): If a bundle of fragrances is on the table, and he takes them to smell them and returns them to the table, if he intended to smell them again, he need not bless again. This is even if he left the house with intent to return immediately. If he went to his job or to pray in the Beis ha'Keneses, this is a Hefsek and he must bless again.

Shulchan Aruch (ibid.): If he intended to return, he does not bless.

Beis Yosef (DH u'Mah): The Tur brings from Maharam that he blesses each time only if he did not intend to return. If he intended to return, he does not bless [again], for he did not divert his mind. The Mordechai (188) says so.

Magen Avraham (2): This is only if he intended to return immediately, like I wrote 639:17.

Kaf ha'Chayim (4): The Taz (639:20, brought below) exempts even if he will return much later. Four others hold like the Magen Avraham.

Magen Avraham (3): This is difficult. All agree that for something that does not require a Berachah Acharonah in its place, if he changed his place, he must bless, even if he intended to return (178:2)! Here is different, for later he smells the same fragrance he smelled before. Therefore, he does not bless again, like one who left his Sukah with intent to return (639:8). See what I wrote in 218:5 and 8:18. Eating is different. Each time he eats a new matter, so he must bless. Based on this, if he returns and smells different fragrances, he blesses again. Alternatively, here no action is missing (e.g. to eat). Once he returns, he smells automatically. Therefore, his intent helps.

Gra (DH v'Davka): The first answer of the Magen Avraham is wrong. See what he wrote in 218:5 (below).

Kaf ha'Chayim (5): The Drishah says that he left friends behind, therefore he need not bless again. Ma'amar Mordechai says that here, friends do not help. Rather, he went only to the doorway and sees his initial place. In such a case, he need not bless again also for food.

Magen Avraham (218:5): One blesses [on a place where a miracle was done for him] once in 30 days. Why does one bless each time on thunder, earthquakes, and fragrances? There, he does not see the same matter each time. Regarding fragrances, even though it is the same matter each time, since he benefits, it is like eating, on which one blesses each time. Ra'avan and Avudraham say that smell is not the matter itself, for it gets stronger.

Mishnah Berurah (7): Even when he smells different fragrances, he does not bless again.

Shulchan Aruch (639:8): The custom is to bless on the Sukah only at the time of eating.

Taz (639:8): The Beis Yosef says that if one left the Sukah with intent to return immediately, he does not bless again when he returns. Birkas ha'Torah is different, for one never despairs from learning. He is commanded to learn constantly! This implies that one blesses again for Sukah even if he knew that he will eat two meals. Why is this unlike a fragrance store? If he intended to return, he does not bless again, even if he left for a long time! Sukah is obligatory only when eating. Afterwards, it is optional. Once he blessed Birkas ha'Mazon, another meal is a new Chiyuv Mitzvah, even if he intended from the beginning. Regarding fragrances, there is no end to the first action.