The thing that says "theft" to me: the presence of other instruments. Trombone? Couple of guitars (or at least the case/bags)... If his band broke up or something, I'd think the players would take their instruments.
He claims to have title to the trailer and receipts for the gear but that doesn't jive up with the pics.
Also, if this was stolen my bet is it wasn't recently.
Edidt PS. Thomas posted a link to reddit where this was discussed; seems someone contacted the seller and got the story. Makes sense. Stand down.