I recently sold a 6505+ head in great condition shipped well packaged with the tubes seperately. The buyer bought the amp in November and is now sending me messages that the amp is struggling volume wise and they've taken it to two techs without being able to resolve the issue. My return policy was 2 business days after arrival. Am I being mean by refusing a refund? Ive offered to help pay repair costs but since they've taken it to two techs it's now costing them as much as the amp without a resolution which I find very odd. There were no issues before I sent the amp and I included a new set of power and preamp tube sets what would you do in this situation?