Yeah, the only way of proving it to get access to their Skypes. btw, why didn't you even consider escrow?
Note that JameRD does not use all lower case anywhere in his forum posts. So it could be that OP framed him, and used all lower case to make it such that members will not consider them to the same person.
Or JameRD intentionally changed his style so that it would appear different to others, which is quite probable.
tl;dr, I think JameRD scammed OP (imo a
70% 80% probability). But it is also possible that it is a false accusation. Only possible way of proving it is getting a trusted third party to access the Skype accounts of both parties.