With most wedding photographers these days, payment is typically due up front...so when the photos/product is delivered, the payment has already been collected and hopefully the check has cleared.
I've heard plenty of stories about clients who didn't like that situation, but then we need to remind them that everything else is paid for up front...the venue, the meal, the dress, the flowers, the DJ/band etc.
If they are unsatisfied, I agree with Mike30D. Try to find out what it is that they don't like and address those issues individually. Offering any sort of refund should be a very last resort, once you go down that road, it's a slippery slope.
Of course, it's important to have a good contract, which outlines your responsibilities and what you need to do you job. For example, 'client cooperation'. You could have something that states that if the client does not cooperate with you during the event, you are not responsible for the quality of the images. These should not be used to cover up for poor work but should be a protection for you, in case the clients really aren't doing anything to help you do your job.