The Gem quotes Mar that "Even if he goes IN and OUT the whole entire day, the Get is Kosher."
The Gem. rejects that we are referring to the 'Sheliach' and says that the 'IN and OUT' refers to the Sofer going out to the marketplace.
Why does the Gem. assume it's the Sofer; there is a 3rd possibility. Namely, that it refers to walk-in traffic IN and OUT of the Sofer's house. Isn't it likely that if people are walking in and out of the Sofer's house one of them might have come there to write a Get? Perhaps even more likely than meeting such a person in the marketplace?!
And althouh only the term 'IN and OUT' is used in English', and the term 'OUT and IN' is not; both the terms of 'Nichnas Veoyotzeh' (used here) and the term 'Yotzeh Venichnas' (Chulin 3a) are used by the Gem.
And since the term 'Nichnas Veyotzeh' is used here, it indicates that it refers to a person who first goes IN and then comes OUT. And it does not apply at all to the Sofer, since he first goes OUT to the marketplace and only then comes IN to his house.
Kol Tuv,
alex lebovits, Toronto, Canada
When we read a Beraisa, we have to bear in mind its context before determining who the Beraisa is discussing. In this Beraisa, there are two people discussed before this statement, namely the Shali'ach and the Sofer. The Beraisa then says "even if he goes in and out etc." The simplest explanation is that the "he" is certainly referring to one of the two people mentioned. The Gemara first suggests that it is the Shali'ach, because the Beraisa said the same terminology " even if he is in the house." Therefore, the simplest explanation is that it applies to him. When this is discounted, the Gemara states that it must be talking about someone who is the only other person mentioned in the Beraisa, namely the Sofer. Only if this would not be possible would the Gemara entertain your explanation.
All the best,
Yaakov Montrose