When products are being exchanged between the two parties, it is safest to have a bill of sale drawn up so this doesn’t happen.
However, if a conflict arises, things can get complicated. This isn’t necessarily a bad thing if two people can peacefully exchange money for an asset. When buying something used, however, the seller might lack a defined process. The salesperson tells you a price, you hand over that amount, a signature might be involved - you know the drill. When buying something new, the establishment from which you are buying that item will lay out the process for you.
