If unit was described as fully functional or no issues responsibility falls on seller, doesn't matter that it may have been fully functional when shipped. The responsibility for faulty equipment always falls of seller unless they can prove shipper negligence. Always pays off to read descriptions very carefully, failure to disclose any issues in ad means seller fully responsible since the buyer is paying for a fully working functional unit. In your case paypal dispute process will end in your favor as long as it wasn't friends and family transaction. People should be careful when using Paypal F&F, absolutely no protection for purchaser.
Who is Liable with Defective Unit
Purchased a used (10 yrs. old) DAC on internet...was represented "as new", in perfect working order. Arrived OK, packed well, etc. Plugged in and unit would not respond to remote input. Works with manual input. Remote is OK...can see IR pulses with my phone camera. Sent to factory repair for analysis...PCB problem. Seller will only agree to pay 50% of purchase price if returned, which is also about 50% of the repair cost...claims unit was just fine when he sent it. Pay Pal transaction. What remedies do I realistically have?