That is frustrating as hell, I know, I've been in that situation myself.
I have also been on the company side of the situation many more times. I worked at a bicycle shop for 5 years out of H.S., was 3rd in command of the place, I had alot of pull there.
I have had customers bring in things without reciepts many times, and if they were cool about it and the product was in the packaging, I would return it no problem because I do know how far a little bit of customer service goes, especially when your business runs on return customers and word of mouth.
I have also had more than one occasion where someone would pull an innertube out of the dumpster, that I threw away myself because it had a hole. The tweeker would go dumpster diving in our trash, pull a tube, then bring it in through the front door and try to return it saying that we sold them a bad tube. I would then promptly tell them to get the out of the store.
What I'm trying to say is, most retail stores today would rather deal with losing an angry legitmate customer than losing money by having a relaxed return policy. It sucks for those who are legitimate and honest, and it's becoming harder to find the stores who can tell the difference between the 2 types of people they deal with.