A: NO! DON'T DO IT!!! The problem is not the neck, so why adjust the neck? The problem is that someone at the store probably tried to set the guitar up for some other customer and took the nut action too low. You will either need to shim up the nut or replace it entirely.
This is a common problem that happens when someone who doesn't know what they are doing tries to do a set up. They screw up your guitar, and instruct you to screw it up more!
There is a very specific order to doing the fine adjustments of a set up and its all based in science - physics to be exact. It starts with adjusting the neck, then the action is adjusted at the bridge (saddle), and finally action is adjusted at the nut. So....if the problem is at the nut, again, why mess with the neck? Theres nothing wrong with the neck...but there will be if you adjust it.
Go ahead, adjust the neck and see what happens. In about a month or two, you'll probably be in my store needing fingerboard work done...which is approximately triple the price of replacing the nut with a custom bone one, and about 10 times more expensive than shimming!
Bottom line: We are the experts. Don't trust your guitar mega store employee, because almost none of them have had any actual experience doing guitar repair. In fact, if you find one who actually knows anything about guitars at all, you should get to know him personally for your future guitar and gear purchases. Apart from that rare situation, I would stay away from mega stores altogether unless you really know your guitars.