As we saw one the previous daf, our Gemara is discussing how it is forbidden to purchase things that are likely stolen. Our Gemara asks for a ruling that would clarify when it would be permissible again to buy from someone who was known to be a thief. (It is worth noting that there are a number of variant readings to this Gemara – some manuscripts have the question focusing on deriving benefit from the thief; others on collecting outstanding loans from him.) In response, the Gemara offers two opinions: Rav suggests that we must wait until most of what he has is his own; Shmuel rules that when even a small part of what he has is his own.
The Me’iri understands that question of our Gemara to be asking at what point can we buy from a known thief, and be fairly certain that we are not aiding and abetting criminal acts by purchasing stolen goods. The Bartenura suggests that the case in the Gemara is one where the thief has repented, and the question is not related to the stolen goods themselves as much as about when we can derive benefit from the thief’s property.
Rav’s ruling that we need to wait until the majority of the thief’s possessions belong to him is based on the common ruling about rov – that we follow the majority. Once we reach that point, from a halakhic standpoint we can assume that anything purchased from him is not stolen. Shmuel does not require a majority of his possessions to be his own, since in any case we are not certain that what the thief is selling is actually stolen – it is only a suspicion. In such a case, once we are certain that some of what he owns is not stolen property, we can work with the assumption that what we are buying from him can be presumed to be without problems.