Have him send the opamps back to you. Then send him his money back and forget about it. Not worth getting yourself upset about. You'll soon forget the money aspect of it, because at the end of the day, that's not worth damaging your reputation over (in terms of negative feedback). Nor is it worth it to be fighting someone over something so trivial. Life it too short.
The other thing that I think about when situations like this occur is that online transactions are risky adventures. Yet, for the most part, they seem to work out just fine. So I look at it as a "law of averages" situation and am thankful when the "deal" that goes wrong is a CD ordered from Amazon.com that never arrives, or a set of perfectly functioning opamps that I have to "eat" because of something - don't know what - but something beyond my control.
That's a much better scenario than selling someone a used pair of speakers for $10k or more and then having them claim there was shipping damage or that the speakers were not as described (in terms of cosmetics) and then having to deal with all sorts of issues, like who pays for the return shipping via a freight service. Thats when it becomes a real problem! (BTW, that was just a hypothetical situation, not something that happened to me).
My point was that if you enter into a lot of online transactions, eventually you'll have a situation where something goes wrong and either: a) you get shafted altogether, as in paying for an item that doesn't show up, or b) you - being the nice and reasonable guy - end up taking a hit on something that you know was not your fault, just to avoid the confrontation and the hassle and embarrassment of negative feedback.
Essentially, such costs can be thought of as self insurance payments. In other words, you enter into a number of online transactions and unless the cost of the item in question is quite large, you tend not to insure. So when you have to take a hit on that one bad deal, remember to be thankful for the 99 good deals that went smoothly. Each of those uninsured good deals on used gear actually saved you much more money (as compared to buying those same items new) than you've just lost. So, in essence, such events are the delayed realization of expected losses; you just don't when they will occur or how much they will cost you.
What you do have control over is how much they will cost you in an emotional sense, and my advice is to minimize that aspect of it simply because it's not worth the aggravation.
The one "bad" deal I had related to selling a CD player via Audiogon. The guy who bought it from me had sent all sorts of emails, telling me how this particular player would represent a dream come true to him, and that he had been saving up for it, etc. My price was $1,200 which was quite fair at that time for a Shanling T100. In fact, I just looked on Audiogon and see one advertised for $1,250 today. This was several years ago!
I was hesitant to sell to this guy, but he kept bugging me. Eventually, I caved in and sold it to him for $1,050. It was dumb of me to give him such a break because it really was worth more. But I like helping people out and have a soft spot for folks who seem to appreciate the same things that I do, but can't afford them as readily. I had replaced my T100 with another one in the new color scheme (at the time) which matched my T200 and T300. So it was pretty cool knowing that my old unit had found a good home.
Two weeks passed, and then the emails started again. "Thanks for sending the T100 so quickly and for including the extra tubes. You really didn't need to do that but thanks. Oh, and I hate to do this, but there is one slight problem..."
As it turns out, the "problem" was, in fact, something that he had known about in advance, because he had researched the T100 so extensively that he knew every last detail about the product. The glitch was that some of the Shanling T100 units had an issue with their remote control not working 100% correctly when skipping from track to track. Basically, it would skip the first note or two of the next track that you moved to. It was a reading error, or delay I guess. So when the track that you skipped to started, you didn't get to hear the first note or two. Something that I could agree would be annoying, but not something I had any clue about in advance.
Yet, he did, and pretended to have just learned about it after he received my T100 and noticed the problem. In other words, he said that he did some quick online research to see if other people were having the same problem and, if so, if there was any known way to fix the problem. It so happened that there was a cure! Some guy in California could make the necessary modification to the Shanling player itself (not the remote) and all would be well.
So then comes the bit about how he got such a great deal on this player from me and that he really didn't want to send it back, but this issue was so terribly important to him and that he didn't receive the benefit of his bargain, and so on. From all that he had said previously about how much he had read about the T100 for years and how he had saved up for one and drooled over the pictures, I was 90% sure that he knew about the potential glitch in advance and figured I was a "soft" person to deal with, and thus he would use it as a post purchase negotiation tactic.
Rather than accuse of him of as much, I simply said that once the guy in California was in a position to confirm that he had received the unit (with pics from the guy in California of my unit showing the serial number, such that I knew the repair was being made), I'd gladly pay for the repair, but not the back and forth shipping which the buyer also wanted me to pay for.
It was a $150 repair, and he wanted another $100 for shipping costs. I told him that at some point, he should obviously be able to see that such a request is unreasonable. I'd be happy to take the unit back and sell it for more money (like $1,200) to someone like myself who listens to CDs from beginning to end and thus never uses the remote other than to press start. That would put me in a lot better position than $1,050 less $250 or $800 less the cost of some tubes (probably another $100) that I threw in for free.
He finally agreed, and when I got the pics of my unit from the repair guy in California, I sent him $150 and forgot about it - except that I've used it as an example from time to time, like now. I didn't want to snatch his newfound prized toy away from him and then get negative feedback about a "problem" with the item I sold to him that was entirely beyond my control and not within my knowledge at the time I sold the unit.
I probably should have taken the player back, but I really couldn't be bothered to have the bad taste lingering in my mind. Instead, I ended up selling a $1,200 item for $900 and chalked it up to the Forrest Gump 'life is a box of chocolates' analogy.
