Buyer made an offer that was accepted then took several days to respond and make payment....no big deal. U5 was shipped the day payment was received, and confirmed delivered on 9-6-19. 3 weeks later, on 9-28-19, I receive message that buyer 'Finally had a chance to try the U5 and Active/Thru switch is creating lots of hum'. I suggested checking power source and confirmed 1-year old U5 was operating with no issues at shipping time. Buyer raises paypal dispute, paypal requires a refund once item is shipped back. When I received item, U5 is working perfectly with no issues; and sounds great.
Highly recommend you have an agreement with this buyer regarding any returns/refunds BEFORE you agree to a Paypal transaction.