Only experience I have is I used to work for rides at a local dealers yard. She was straight up and horses were as described. Therefore anything not suitable would be sold through those groups instead. This was a while ago though and I've not seen her sell anything on there recently. She did buy 1 or 2 from those pages though without problem (again going back a while)
Can your friend contact the bank at all? I'm presuming it was paid by bank transfer in which case getting it back depends on the recipient account holder releasing it, which if it was a scam is unlikely! May have to chalk this one up to bitter experience unfortunately.