Not really that much you can do to a keyboard...

But they might be leery of letting you near their computer system! Perhaps it's worth d/l'ing the update at home (and the update instructions) and just take it to the store.

You make them aware that the sale is predicated by you being able to test how well it works with your iPad, and that that is determined by it being up to date, I doubt any dealer would turn you away from updating it.