Good fakes feel substantial, accurate timekeeping and high quality of watch dial. Someone even told that the only way to reveal they are not genuine is to flash back. The majority of replicas now uses proper mechanical movements and sometimes boasts transparent 'exhibition' backs so you can see the wonders of horology for yourself. Even the word 'replica' suggests that the product you're buying is legal-ish - a 'tribute' to the original rather than a blatant rip-off.