Hi. Do I have to kasher a new pot that I bought in a gentile department store because they accept returns so it could be it has been used by a gentile?
Thank you for your question.
If you want you may kasher any new pots etc. that you buy, and there is nothing wrong with doing so. Especially metal pots that have a shine to them, as there are poskim who say they should be kashered, even by pouring boiling water over them. This is because the hot oil that is poured over them may not be kosher. Others disagree, and in the States most people are not kashering new pots.
Regarding your question though, in consultation with a kashrus professional, if you are buying the pot from amazon or another reputable place, the returns are not resold, but are sold to a different company who will sell it as used. However, if you are buying from a place like e-bay, where anyone can sell anything that they like in any condition, then your point is valid if the seller is selling it as “like new” condition. If the seller however is selling it as “new” then you can assume that he is not lying and selling a used pot as new. If he does sell the pot as new when it isn’t, he is running the risk that if he gets caught, someone can make a serious complaint against him, therefore he wouldn’t want to do something like that.