It is really up to the business owner. I'm in LE, and I really appreciate some of the special pricing that I can get on guns. Honestly, I think these prices are really made available to us through agreements that the merchant has with the manufacturer (Blue label Glocks, for example).
Anyway, I think it can certainly work to the seller's advantage. The local police supply store in this area gives a decent price on the guns they sell to cops. But, they also sell leather, holsters, accessories, and every other imaginable piece of police equipment. As such, they might lower the price on the gun, but they sure make up for it when you go to buy the rest of your gear.
My department provides us with a belt, pepper spray w/ a holster, a radio, one set of handcuffs, a glove pouch, and our uniform shirt/pants. We also get an allowance towards our ballistic vests, but mine was still an extra $250 out-of-pocket.
When I started I was also required to buy: Gun, holster, flashlight, flashlight holder, belt keepers, radio holder, SAP, boots, baton ring, under belt, etc. These items add up quickly, so the gun discount was much appreciated when I was a rookie!