"Rules say no response within a certain time, I think it's 72 hours, is an approval. Joke's on them, not the good guys."
Yes, but if the instant check shuts down, it will play havoc with gun shows.
To some extent, but only FFL's are required to run NICS even at a gun show (at least if you live in a free state), and in my experience, the FFL's are all local shop owners anyway.
So give the guy a business card with the model and S/N written on the back, and in three days he shows up at the store and picks it up.