Got the whole story from the bike shop. There won't be any warranty with the frame at all, specific to the tube being dented. The owner is sending pictures via email in the next few days, and I'll check it out with a frame repairer or two. It's a great deal, or it appears to be. He (the dealer) is very confident it will be a good starter tandem, especially for the price. But without a warranty backing him up...well...