ebay will make sellers of fake coins/cobs give refunds if requested but many people are ignorant and don't know they were taken until it's too late.
I used to buy lots of Spanish cobs off ebay and I never got burned. But today I rarely do it. I try to locate actual treasure hunters and buy from them. I want my cobs ocean encrusted and mostly uncleaned.
I also used to buy rare paintings off ebay until I got burned big a couple of times. The fakes were so good it took me a couple of years to discover the truth.
Today on ebay probably not 1 claimed painting in 10,000 is a genuine original 19th to early 20th century painting.