e.g. I don't plan on prorating monthly subscription cancellations but this won't result in any severe amount of money gone if someone tried to abuse unless there was some giant, coordinated scam. In the latter case, whoever's credit card got stolen would likely do a chargeback anyhow.
And as for customers taking advantage of it, I really think the number would be less than of people who didn't take advantage of it when they weren't satisfied. Personally I know of one small rebate that I didn't end up cashing in because I never got around to it, and I would have to be really unsatisfied with a product to go through the time and hassle of asking for my money back.
Wikipedia Link:http://en.wikipedia.org/wiki/Rebate_(marketing)#Some_redempt...
I've only had one customer ask for it.