I go to a local Pep Boys if i want a set of warrenty tires. I had a set of tires wear out at around 20K miles on a ZX2 and they took the bald ones back and payed around 80% of the new tires cost, wich to this day are still under warrenty. On the warrenty receipt at the bottom it stated "alignment recommended" wich wasnt done. They still took them back no questions asked 20K later, and they were bald as possible. Not flat bald, just on the outside edges wich indicated a major alignment problem.
At a shop i used to work at we had to do repairs on many cars that had been messed up at Wal-mart. Most of wich were supposed to be simple "DUH" jobs that turned into nightmares for the customers. Im not saying ALL wal-mart employees are going to screw up, just saying its not worth taking the chance especially if you drive an SUV. They have much more potential to roll when and if a front tire goes south at a high rate of speed.