1. The Gemara says that a person does not want to be known as an evildoer who does not pay back his debts.
2. An idolater is presumed to be a thief and a liar.
3. Rabah: A craftsman has a Chazakah if the item was given to him without witnesses.
4. There is a dispute about whether a deposit made with witnesses must be given back with witnesses.
5. Abaye argues with Rabah (#3 and #4).
A BIT MORE
1. This is as the verse in Tehilim (37:21) states, "An evildoer will borrow and not pay."
2. This is as the verse states, "That their mouths speak falsehood, and their right is a right of lies."
3. In such a case, he is believed to say that he bought the item, since he could have denied that he received it.
4. Rabah maintains that if the item was given to the craftsman in front of witnesses, he cannot claim that he returned it; he must return the item in front of witnesses. If he cannot bring these witnesses, it is presumed that he still has the item (if the owner claims that he does).
5. Abaye says that a craftsman can make a Chazakah whether the item was given in front of witnesses or without witnesses (see the Rashbam for the explanation of the Mishnah according to Abaye), and that a deposit made with witnesses does not have to be given back with witnesses.