FYI, I know that at Micro Center, based on information from someone working there and depending on the manager, they will most likely (in this order):
1) Give you an even exchange for the same spindle if you have burned one or two discs.
2) Give you a gift card for the full amount if you have burned one or two discs.
3) Give you a full refund if you have only burned one or two discs, if you complain a little (ymmv).
4) Give you an even exchange for another spindle, and take out the number of discs missing (if you have, for example, burned 20 out of 100 discs).
Pretty fair, IMHO. I have no idea what the cutoff point is on how many discs are missing when you return it...