1) Find out who the authorized dealers are that are the closest to you -- for every machine you are considering. And find out if they're reliable and fast. Go to a LQS and start talking to the other quilters that are there. They'll tell you the best info on the repairmen.
2) go to the show and try out as many machines as you can. If the price is better than elsewhere, buy --- an authorized repairman can repair a machine no matter where you bought it.
3) Don't fall for the "you can send it to the factory" line I've heard......it'll cost you a fortune (maybe) and it takes weeks to get a repair job done.