This seems like something that I shouldn't have to explain and yet here I am writing to you about things that you shouldn't buy if they have had a previous owner. I have compiled my list by rummaging around Twitter for what I can only assume people have purchased second hand and that's how they made the list.
It's not very often that I'm browsing Craigslist for a new pet or anything for that matter. But sometimes I do hop on there just to see what kinds of things people are trying to give away, you never know what you're going to find after all.