No offense, but people are "sue happy" because of situations like this that are 100% your fault. Yes, you now have a buyer who is aggressive, but this would have never happened had your ad been truthful, i.e. I upgraded the HD myself.
Here's the buyer's dilemma. He thought he was buying an Apple OEM drive with X capacity, and he paid up for it. Now, if you only exchange drives, he's short because while he gets an Apple OEM drive, he gets less capacity than he thought he was buying. Your last offer should be send him the Apple OEM drive and a little $ to makeup for the lower capacity.
You have a lot of MR history so am making sure you understand that you will lose. PayPal/eBay is buyer friendly, and your ad did not match the description. Unfortunately for you, the buyer now has emails where you acknowledge that you didn't mention the drive upgrade. Lawyer or not, if the buyer is as aggressive as I was with PayPal and/or his cc, you're going to lose. If he is beyond the time limits and chooses to pursue a small claims case, you will still lose. He has your recent emails.
I initiated a refund after 4 months, my buyer had closed his PayPay account, but I still got my money back since they used a collections agency to track down the seller.
The decision is up to you, ride the lightning if you wish, but you're dickering over a stock HD (that reads like you no longer use) and maybe an extra $20-40.
Good luck.
I still don't get it. I listed an item with an i5 CPU, 4GB RAM, 500GB HDD, etc. I said it was all in perfect condition and all under warranty until May.
I did not specify if the items were stock, 3rd party, used, or anything else. I provided the most accurate information in my ad. It was an honest mistake that I forgot to mention the HDD was 3rd party, but it should matter considering everything lined up with my terms and details of the sale.
Edit: My issue, or rather your folks' issue, is that you aren't thinking logically. I offered A product under B terms. I provided A product with B terms.
Let's say you were selling a car that was still under warranty. You replace all the tires due to damage with brand new tires, better than the original tires that were included, and warranted longer. You didn't disclose that the vehicle had new tires. Would the buyer have a right to return the vehicle because it wasn't disclosed that you used aftermarket parts? Even though everything is covered under a warranty longer than it would have been if they were the original tires?
The argument that is being made does not make any sense.