The gemara in kesubos talks about a case of moneh li biodcha where malvi is bari that loveh owes him a maneh and loveh says shemah maybe he doesnt. R' Nachman and R' yochanan say okie mamon bchezchas mori and Rav Huna says Bori vishemah. The mishnah in bava metzia (daf 100a) says if lokech says you sold me big field and mocher says shemah I sold you small field the lokech gets the big field. Is'nt this a question on R' Nachman b/c it seems like from the mishnah that we say bari vishemah bore odef?
A yid, New York
Tosfos (DH "Manah Li") says that the case here in Kesuvos is where the borrower says that he is unsure if he ever borrowed money from him at all. In a case where he admits to borrowing money but is unsure if he paid back, everyone agrees he is obligated to pay (see Bava Metzia 118a). The case in Bava Metzia is clearly such a case (as he admits to the sale and is merely unsure which one he sold), and is the reason why Bari v'Shema does not apply there.
All the best,
Yaakov Montrose