I bought my motorhome out of state. After a few phone calls I was pretty sure I was dealing with an up and up person, she also gave me the name of the local shop where all the work had been done on the motorhome. I called and chatted with him, and while not a full inspection or anything I at least felt convinced that it was well maintained. I suppose it could have been an elaborate scheme between the two of them, but I didn't get that vibe lol.
I didn't do a deposit (seller didn't ask for one), but I did rent a car and drive 8 hours to go check it out. Paid cash, returned the car to a local airport, and drove the motorhome back home.
I do think though that at least the threat of a local mobile mechanic coming out to inspect should be used. See if the seller has any negative reactions to the idea or not.