When does seller's responsibility end?


I'm sure this has been discussed before, but a search could not find it.
I sold a Naim DAC (mentioning this because Naim is notoriously reliable) to someone on November 26, shipped on November 27, 2012.
Did not hear anything one way or another until December 19, when seller emailed to say one USB input would not work with his ipod. Well the input worked for me when I had it. I asked him to be sure he was doing everything correctly, including checking for bad cable. I am not sure the input really does not work.
No word again until December 25, when he asked if I would pay for repair. I answered no, because I felt the time period had been too long and my responsibility was over.
Now he has initiated a dispute/claim against me on Paypal. They have put my account in the negative for the amount of DAC until they resolve it.
Sorry for the long post, I just wonder if there is a consensus on how long a seller should be responsible for "sold" gear. I say a week, maximum.
What say ye?
muzikat
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I would say the seller's responsibility ends when after plugging it in/setting it up it works as described.  To be generous I would give the buyer 1 day assurance that all is well.  It is the buyer's responsibility to immediately check it out upon arrival.
"....I would say the seller’s responsibility ends when after plugging it in/setting it up it works as described. To be generous I would give the buyer 1 day assurance that all is well. It is the buyer’s responsibility to immediately check it out upon arrival..."

+1 ....full stop.

OP fact circumstance as described with an intervening month until Buyer’s sudden wailing started sounds more IMO as either
(a) buyer’s regret,  or
(b) buyer f****ed it up after he played with a month.

so ..... sayonara and tuff noogies to Buyer and no further seller responsibility(ies) ....full stop.
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After 4 week´s correspondence with eBay and after 4 reports on buyer´s inappropriate behauviour eBay finally ended the case for my favor. Every time I replied them I referred to my ad and the photos in it. They had nothing to hold on. One can´t con an honest man.
Yes, eBay really LOOKED at my ad again and said it wasn´t my fault and my money was released. Buyer was accusing that I hide marks/imperfections on the item. Even most of the biggest marks/scratches are actually visible in my ad. Of course it wasn´t my fault, I knew exactly what I had been doing all the time, buyer just tried to cheat and crab money from me but failed. In fact, he had earlier before sale´s end suggested that I could pay half of shipping that would be very expensive for a 45 kilos parcel and the actual cost was still unknown. At this point I went suspicious but agreed to pay half, as a gently gesture. Funny, he never thanked me about this...

After sale buyer made several basic mistakes, not accepting return, demanding "extra services after sale" and "Misused the programme to claim an item was not as described". In frustration when he obviously realized that eBay won´t play the game he had planned he had left a negative feedback. His biggest mistake was "leaving an inappropriate feedback" when case was still open/unsolved. Furthermore, eBay removed that negative feedback right after.

Great, there´s still common sense left but they held my funds for four weeks. That was really bad because I really have no other funds at the moment. I told them that my economy is seriously harmed.

I learned my lesson. I immediately withdrew my money to my bank account and never will sell anything expensive there. And won´t be PainPal´s fool anymore. What a bloody waste of time.