Stores want your business. Even at chain stores, managers have a lot of leeway to keep customers happy.
Two weeks ago I needed to buy a new mop. The one I'd bought at Big Lots had broken within two times of using it, so I wanted one that would be better quality. Sack and Save had a nice looking one in their ad for $7.99. When I got to the store, the only one that they had that looked like the one in the ad, was marked $12.99. I asked the manager to show me where the one in the ad was. He couldn't find it either. I knew that if I stood in the aisle looking uncomfortable for long enough, that he'd try to keep my business. He walked me to the front of the store and told the cashier to give me the $12.99 mop for the sale price. So I got a much nicer mop than the one in the ad, for about half the price.
If you are at a store trying on clothes, and you notice a defect with your item, ask for a discount! I know that Sears will almost always give you 10% off for an item with a little stain or a little rip in the fabric. The same is true at the grocery store. I love to buy marked down milk and freeze it. At another grocery store the dairy manager asked me if I was finding everything okay. I told him yes, except I was hoping they would have some milk marked down. He went and got a marker and marked some milk down to 99 cents for me. Meat managers will do that as well.
I rarely have anyone tell me that they can't mark an item down, but even if I did, it didn't hurt to ask!