+1 on that. I'd say it's equally important for parts too. In these enlightened times of people being more than happy to buy online a range of items of varying price needs stocking. It's all very well having a glass display cabinet full of gucci gun jewelry but if someone just wants a clone part because that's what they can afford, you need to stock them too.
Make sure your supplier can get hardware to you at a sensible cost that won't screw the pooch on margins too. My local shop for instance buys a lot of stuff in at a relatively high cost. By the time they put on a margin cheap, imported clone parts cost almost what the high end branded stuff does!