Sounds to me like you've already figured this out as a scam.
1. See the AS in person
2. Look it over very well, ask to see the title
3. Cash up front, take delivery with the cash
4. Don't worry about offending anyone. If the deal is legit, no one will be offended. If you were selling, would you be offended if someone asked detailed questions?
5. Get the title (his name and address should be on it) and bill of sale. Take delivery on the spot.
Usually, you can tell if you are there in person, about the seller. If there is any doubt in your mind, walk away. There are other AS out there for sale. Be cautious. The guy I bought mine from was very open, I asked him every question I could think of. I left him a check as a deposit. He said that was more than he had left with the first owner. Turns out, he was 2 years behind me in the same high school, looked him up when I got home.