I dont know why I cant post a "coin auctions help" link but if you search your browser "detecting cleaned coins" the first link is to coin auctions help with a basic description of cleaned coins.
Im no "expert" at detecting cleaned coins. I dont know how many tens/hundreds of thousands of coins I've looked since the early 60s. There can come a time, with enough knowledge, exposure to, and practice with coins when you'll begin to be able progressively and more identify cleaned coins.