If you allow customers to take down guns then they will occupy much time at the counter doing that. I don't want to follow behind one of these guys and purchase something they had been fooling with....
At the local shops I've been to, there is no problem taking as much time as needed. I've waited over an hour for my turn, but then can take my time. The shops want the customer to be satisfied with the experience, regardless if you purchase that day. Having said that, you can't please everyone.
They may not allow take down and dry fires (OK, the shops near me typically allow racking and dry fires), but they will also bring out multiple guns to allow you to compare (assuming they have it). That includes long guns.
I do most of my browsing online. I read some reviews, watch a few vids, then narrow down what I want. Then the hunt begins to find someone nearby with stock. While shipping may be free, we pay tax and transfer fees here in CA. Extra fees apply if it's not on the Roster of Guns Not Unsafe (until 1/1/2015). So by they time you get done, that great deal you found on GunBroker vanishes. Ten round mag limits can also complicate online deals here.
In the end, market forces reign supreme. Don't like the policy, shop somewhere else. Just realize while you may think "screw them, I'll take my business elsewhere", they may think, "thank God that jerk left".