(Since it may be relevant, I am in the UK.)
There are many sites where people can place items they want to sell to potential buyers. For example, gumtree or facebook marketplace. One potential worry for buyers is that they may buy something (e.g. a phone) with cash off someone on one of these sites, and then have the person make an insurance claim on this item and say it was stolen (or alternatively, the item was stolen to begin with, and the seller gets caught). Then the buyer has lost their money, and (I assume) the item must be returned to the real owner.
My question is, how can a buyer protect themselves from this?
To prevent the person from saying I stole it off them, perhaps it would be sufficient for them to give me the receipt they got from the store that they purchased the item from. Another alternative is to only pay by card (not cash), but this significantly reduces the number of items one can purchase, since most sellers seem to accept cash only.
I am not sure how one can prevent against accidentally buying stolen goods other than watching for signs (like the seller being in a rush to sell) and not buying if it seems dodgy.