Rabbi Yehudah's opinion is that a worker could take an oath for an employer (and collect the funds), and the Gemara works to figure out the source for this halakhah. But that kind of dispute can't be about wages... Also, in the name of Rabbi Yehudah - when someone leaves another home with objects concealed beneath his clothes - that's suspect (when he says he bought the items), unless it's actually not suspect for a whole host of potential reasons.