anjulie,
It is likely that if you buy freshwater pearls from Chinese sellers on eBay, they will be real FWP.
Be aware that unless the listing states that you will get the exact item in the photo, it is likely that the photo is merely representative. The pearls you actually receive may be of poorer quality. Also, be wary of out-of-focus photos as they tend to conceal the fact that the pearls have a poor surface.
If you order so-called "akoya" "south sea" or "Tahitian" pearls from Chinese eBay sellers, there is a very good chance they will actually be freshwater pearls.
Avoid any listing that includes the word "shell" because so-called "sea shell pearls" are really imitations.