The major US rental stores offer a 7-30 day exchange policy if you purchase a bad previously viewed disc. I forget all the policies. Essentially, if you buy a previously used disc and you haven't checked it out within 7 days to make sure there isn't a flaw then all I can say is shame on you.
I have a lot of DVDs that I purchased as previously viewed discs for really really cheap prices. I paid a heck of a lot less for them so, yes, some are worn but they play fine. Some of them I don't care about but I always make sure they are error-free when I get them. The ones that I need to make sure will continue to play are the ones that immediately make a backup of.
Anyway, the major stores should check the discs for scratches, etc, before you purchase the used disc. If they don't check then ask them to. If they refuse to or you believe they aren't really checking then you can walk away, ask to speak with a manager, or buy it and check it out at home. If it is flawed then return it within the specified return period.
Even if the store checks it and it appears flawless it is still your responsibility to scan the disc for errors and check it for playback issues and immediately return bad discs. Of course, always always ask for an exact return policy before purchasing.
In short...
- In the US I have found there to be no differences between Region 1 rental discs and Region 1 retail discs other than that some Region 1 rental discs that are Blockbuster exclusives may have different preview garbage than the same disc if you purchased it at a retail store such as Wal-Mart or from Amazon or some other retailer.
- Always make sure the disc you purchased is error free and return it if you find a problem.
- Make a backup as soon as you find it is error-free if you wish to protect your investment which you paid way less for to begin with.
If you don't test your discs, protect them as well as you can, and back up the ones you wish to keep safe since they are already worn then you can't blame anyone but yourself.
Btw, I'm not aiming this post at any specific person. I'm just saying all this in general to everyone.