First, you'll need a working battery and a card, which the shop may or may not be willing to supply.
You can check the RF by seeing that the images coincide at infinity when focussing on a distant object (the further the better!). For close focussing you'll need to take some shots, and it's not easy to do a careful check quickly in the shop.
To check the VF alignment, again, you'll need to shoot something and check the playback. I checked mine in the shop by photographing some product shelves and a film fridge. Make sure you're standing square on. Any serious error in the VF frame should be readily apparent on playback. This is only really to check that the framelines are parallel to the captured image, i.e. edges line up ok to the edge of the frame. You can't really get a clear idea of the accuracy of the actual framing from a casual test like this.
Unfortunately, it's not really very easy to check for stuck or dead pixels using this approach. For that you'll have to download the images and look at them at 100% on a computer. You could take a laptop into the shop...
The bottom line is that if the pix look ok, you're probably not going to have problems. Unless the viewfinder is really off (and some are!) then I wouldn't worry too much. You can get too concerned about small errors. I know it's an expensive piece of kit, and I've had problems with mine, but I'm still very happy with it. It's *so* much better than anything else out there that I've come across in the digital world 🙂