Scams when selling on Craigslist or ebay

I had friend who had the scam ran on him he deposited the check and it cleared he shipped package refunded the over payment 3 days later his bank withdrew orig check amount out of his account n he lost out on part and the cash , I think in my case they had no interested in the part and shipped it wherever , they were looking for the difference in over payment being sent to them . In my eyes if you can’t speak to them on the phone about the actuall part and they haven’t a clue to what the part is or what there building w it it’s a scam , the lady on the phone after I told her I was aware she was scamming me hung up after initial saying she wasnt a scammer and was insulted .she had no idea what a std 3 13/16 race case was .... couldn’t even spell cases correctly in email . It was a buell billet dragrace case for 114 inch motor. Seller beware. Anything over 200$ I try n talk to someone lok next giy that hit me up for them chewed my ear off for 20 minuets aboutwhat he was building and we had a smoothtransaction