I was assuming more that the guns had been tested at some point before they made it to the shop... The loud noises would be all in Lucas' head. Unless a car happens to backfire while he and Sam are talking. :P 

I'm not at all on the up and up concerning gun manufacture or sale. I just did a very quick google search that mentioned four different options for gun availability in Toronto, one of them was renting.... Admittedly, this was talking about gang members getting guns, so I dunno where they'd go to rent one, but I just figured if it's on the first page of google, there's going to be at least one either in-the-know or idiot person wandering around wanting to rent a gun. It would make a lot more sense for a shop to allow gun rentals if they can keep them close and see them being used at a range. I forgot about ranges. lol