Shlomo Zalman, to answer your question properly, we will have to learn the whole Perek in depth.

1) I did once hear that the Me'iri writes somewhere that most of the Halachos in Maseches Bava Basra are based on Sevara, logic. I cannot find at the moment where the Me'iri writes this. However, I understand the idea behind this to be as follows. We find that Bava Kama opens with the damages of "ox," "pit," "fire," etc., which are stated explicitly in Parshas Mishpatim, and then, in Bava Metzia, we have the Mitzvah of returning lost property which is also learned from explicit verses. Bava Basra is different because we do not have so many Halachos which are learned from verses.

2) However, after saying that, it should be pointed out that the third Perek does open with Rebbi Yochanan saying that the Chazakah of three years is derived from the ox which is considered "Mu'ad" if it gores three times. The Gemara proceeds to cite further sources for the three-year Chazakah. We observe that the Gemara is trying hard to find the source for Chazakah.

3) The Mishnah in Kidushin (26a) tells us that land is acquired through money, a deed of sale, or Chazakah (Chazakah in this context means, as Rashi there explains, that one locked the gate of the field to show that he is acting like owners do. This does not refer to a 3-year Chazakah). The Gemara derives the above Halachos from verses.

4) The Gemara in Bava Basra (37a) cites the opinion of Rebbi Akiva that when someone makes a sale he does so generously ("Mocher b'Ayin Yafeh Mocher"). This must be an estimation of the average person's intention when he makes a sale, so it is a Sevara about public opinion.

5) After searching more for that Me'iri, I have still not found it, but I have found that the Tiferes Yisrael writes something similar. It must be very significant that the very last Mishnah in Maseches Bava Basra (175b) tells us: "Rebbi Yishmael said: If someone wishes to be wise, he should occupy himself with monetary law, because there is no similar area of Torah, which is like an overflowing spring."

6) The Tiferes Yisrael, at the end of the Masechta (#85), writes that there is nowhere else that the Torah granted so much permission to human intelligence to have the liberty to research penetratingly and to decide according to what seems logical, as we find in monetary Halachah. The Torah opened up here an "unlimited inheritance." The Dayan is entitled to weigh up and judge according to his intelligence. The Tiferes Yisrael writes that the majority of the vast field of laws of plaintiff and defendant are included in a few words of the Torah in one verse (Vayikra 19:15): "Judge your fellow righteously."

7) The Tiferes Yisrael writes that the Sages of the Mishnah and Gemara, thousands of the great minds of the nation, gathered together and laid down principles with which to make rulings, but the Judge is still left with space to use his own logic, sometimes making a distinction as delicate as a hairsbreadth. This is why studying monetary Halachah sharpens one's intellect. In areas of the Torah dealing with what is forbidden and what is permitted, if one is unsure what the Halachah should be, one may be stringent in a case of doubt. In financial matters one cannot do so, because if one is stringent on one of the parties, this means that he is lenient on the opponent, which is unfair. Therefore, one must put all of one's efforts into achieving the absolutely correct ruling.

8) We learn from the Tiferes Yisrael that the source for thousands of Halachos is from three words of the Torah: "b'Tzedek Tishpot Amitecha" (Vayikra 19:15). The Tiferes Yisrael does not write that this necessarliy refers more to the third chapter of Bava Basra than to other chapters, but it is meaningful that the last Mishnah in Bava Basra teaches us this special nature of monetary law, because Bava Basra is so full of Halachas based on Sevara, and it is well known that the third chapter of Bava Basra is special in its content of Sugyos which are based on fine logic.

Kol Tuv,

Dovid Bloom