I don't know how some guys do it. I have talked with other guys who buy "lifetime warranty" parts, expecting to be able to take them back forever. Each time I have taken a lifetime part back, they won't give me the receipt back. I have never argued with them, since I did get several years out of the part, but I did take note of it. Most of the time it's exhaust system parts. I put a complete Walker exhaust system on my wife's Honda and it had a lifetime warranty, and it wasn't cheap. About 6 years later it had a hole in the muffler, and since it's a welded system, about half of it had to be replaced. I didn't even have the receipt, but they had a record of my buying something that was about $300, so the guy was nice and replaced it for free, but he said this would be the one and only time they would do it.
I don't take much stock in the "lifetime warranty" from my experiences, but it can give you some benefit sometimes.