I've sold a good amount on ebay, to protect yourself do the following:

• 1. Make sure the order says it is eligible for seller protection. If it does not, or if it says partial protection, you are taking a risk that if the buyer file a claim, you really have no recourse.
• 2. Use signature confirmation. It is only ~$2 extra but once it is signed for, it is the responsibility of the buyer and they cannot claim they did not receive the item.
• 3. Be sure to always provide detailed pictures and an accurate description or you could be subject to an "item not as described" claim. Those generally close in the buyer's favor and you have to pay to get the item back.
• 4. For computer parts specifically, if you can provide some sort of picture showing a test or something verifying the item works before you send it, the buyer will most likely not be able to claim the item did not work. For your own records, it may be better to take a video showing the to-be sold computer part in the computer, running a test or something, and then showing the results/it working on the monitor all in one clip that is not cut. It would be even better if you say the date and/or show an online calendar or something. This would prove that as of that date (which should be right before you sell it) the item was working so if the buyer claims the item is not working, which I've seen more often than you think, is due to user error or that they are simply lying.

That's basically it, some of this might be overkill but I have never had anyone successfully win a case against me.