We bought a Western Digital external hard drive for Jen's computer while we were in Omaha. I hooked it up when we got home and it was dead on arrival. I called for an RMA ("return material authorization" - basically permission to return it to the manufacturer) and got the replacement a few days later. Unfortunately, they didn't include a pre-paid shipping label to return the defective part, and the customer service guy wasn't too keen on giving me one. I wasn't asking for anything unreasonable or that they just justifiably deny, and here's how I got one anyway:

CS guy: It's not our policy to give out shipping labels. It's the customer's responsibility to pay for shipping.
Me: It's not this customer's policy to pay for shipping products that were dead on arrival.
CS guy: I see your point, but that's not something we normally do.
Me: OK, but I'd sure appreciate it. I mean, I did you a favor by calling you instead of returning this to the store. I didn't know I'd have to pay for it.
CS guy: Well, we don't do a very good job of telling you that on our website. I can ask my supervisor, but I don't think he'll do it.
Me: I'll hold.
[5 minutes go by]
CS guy: Sir, this isn't something we do, but since these are special circumstances, we'll do it just this one time. You'll get it within a week.
Me: Thanks! Oh, and can you extend my deadline for returning the broken one by a few days since I don't have the shipping label yet?
CS guy: (sighs) Yeah, OK. You can have an extra 10 days.

Note two important things: first, I was polite; second, I was assertive. Failure on either of those would have wrecked the whole deal.