The Gemora implies that if the buyer always buys for plowing, we assume this sale was for plowing as well, and the sale is void. Rashbam says that this is true only when the seller knows the buyer, and therefore had to assume that he was buying it for plowing. Rashi (BK 46a) says that even if the seller does not know the buyer, if we know that he only buys animals for plowing, he may void the sale.
The Gemora also implies that if the price of oxen for plowing is different than the price for meat, then the sale price can prove what the purpose of the purchase was. Although the Sages (77b) rule that we cannot use the sale price to prove what was included in an ambiguous sale, they agree that the sale price can resolve the doubt in the sale of an ox. Rashbam explains that in the earlier case, the simple understanding of the sale (for a plow attachment) would not support the buyer, and the buyer must therefore prove his position. Simply paying a higher price is not a sufficient proof. However, in the case of Shmuel, since we already know that this buyer does sometimes buy oxen for plowing, the sale price can resolve that this sale followed a normal pattern of purchase.
Tosfos (92a vLechze) says that in this case, either side has a support to their position – the buyer has a majority, and the seller has possession. Therefore, the sale price is enough to tip the case to either one's supported position. In the earlier case, the sale price is not enough to support the buyer against the seller, who is supported by both majority (of people who mean only to the plow accessory) and possession (of the purchase money).
The Ramah (quoted by the Tur CM 232) states that Shmuel only precludes following the majority when it would remove money from one currently in possession. Therefore, in the case of the goring ox sold, we allow the seller to retain the purchase money, and may not remove the money based on a majority. However, if the buyer has not yet paid, we allow the buyer to retain the money.
Tosfos (B”K 27b Ka mashma lan) asks how Shmuel is consistent with the fact that we follow majority rule in monetary court cases. Tosfos answers that in a court case, the minority is subsumed in the majority, and neither party is considered in possession, since the court has the power to remove money from anyone's possession.
The Terumas Hadeshen (314) quotes Tosfos saying that Shmuel only precludes majorities that are based on general rules (deductive), but not observed majorities (inductive). This will explain how we can follow a majority in a court case.
The Ketzos in Kuntras hasefeikos (2) quotes the Maharam Chaviv, who explains that the dissenting judges nullify their opinion to the majority opinion, and therefore we are no longer following merely a majority. The Ketzos himself (3) explains that Tosfos is saying that a court has the power to nullify a litigant's possession. Since Shmuel only precludes majorities in monetary halachah due to the possession of a litigant, a court's majority is applicable in monetary cases.
Rav Shimon Shkop (Sha'arai Yosher 3:3) explains Tosfos's explanation of court majority. He states that Shmuel's principle is based on the fact that in monetary halachah, we follow possession, due to simple logic. To defy the current possession, we need a clear proof, and majority is a Torah rule, not a clear proof. However, the Torah rules for a court mandate that its decisions are decided by majority. Once that is decided, the court has full power to render and impose judgments, even in monetary halachah. [See also Chidushei Rabbi Shimon Shkop BK 27, where he explains that court rulings are an attempt to arrive at an intellectual conclusion, based on a majority of opinions. Once that intellectual conclusion has been reached, it has full force in all areas of halachah].
Rav Dovid Lifshitz (Chulin Shiur 22:2) explains, based on Rav Shimon Shkop, that Tosfos means that the minority is subsumed in the majority, just as a minority of non kosher meat is subsumed in a majority of kosher meat. Once that occurs, the court is not simply a majority, but a full unit, all ruling the majority's conclusion. To prove this idea, he notes that if a court of three imposed a judgment based on a 2-1 ruling, if the ruling is reversed, all three judges must equally make amends. This indicates that even the dissenting judge is considered to have ruled the majority's opinion.
Tosfos (Kesuvos 15b l'hachazir) says that Shmuel only precludes majority in a case where the buyer willingly gave his money to the seller, in the context of a sale. To remove that money requires more than a majority. However, in the case of a lost object, whose owner never willingly parted with his property, we do apply majority, to decide if it was lost by a Jew or non Jew.
Tosfos (Sanhedrin 3b Dinei Nefashos) asks why Shmuel does not apply majority to monetary cases. The Gemora proves that we follow a majority of judges in monetary cases with a kal vachomer (a fortiori) from capital court cases. Tosfos asks why this kal vachomer will not apply to Shmuel's case. Tosfos further explains that we apply even deductive majorities in capital cases, and therefore should do so in monetary halachah, as well. Tosfos answers that Shmuel only rejects inferior majorities in monetary halachah, but accepts bona fide majorities in all areas of halachah.
See Bach (CM 232) who explains that an inferior majority is one where only one aspect of the case is a majority. For example, although most oxen sold are for plowing, most buyers buy oxen for meat. A buyer who buys oxen for plowing buys many more than any individual buyer who buys for meat.
See Shev Shma'atsa (4:8-9), who explains that Tosfos in Sanhedrin and Tosfos in Bava Kamma disagree on whether a bona fide majority can be used in monetary halachah.