I'd suggest that you should (1) have the dealer come to your studio with the back, which many of them will or (2) if they won't, pay to rent the back for a day and get them to apply the rental fee to the cost of the back if you buy it. There's really no excuse for them to be unwilling to come do a demo at your studio, though, given the size of the purchase. I know my local dealer (Dodd Camera in Cleveland) would do so.
I will be purchasing a new Phase One digital back within the next couple of weeks. Before I leave the dealer's showroom with the back and before I plunk down the rest of the $$ to pay for my db, how should I test the back? What should I look for in the showroom before I take it back to my studio for more thorough testing. What details should attend to before I leave the dealer's showroom before I take possession of the back?