sold a transmission now having buyer problems

Kinda makes me wonder why the original tranny was baked in the first place........
If it was leaking lines to the cooler, it's his baby, not yours.
Maybe it's the way he drives it?
You have no control over that, same goes for the installation.
He could be an animal when it comes to spinning the tires, neutral drops, etc!
How do you know for certain how it was driven after you sold it and was installed?
Look, he paid the price for a used tranny, and it moved the van obviously at least 100 miles, at 120 bucks, he got what he paid for.
I bet any wrecking yard on this planet would tell him to pound sand, and that's what i would do too in this circumstance.

Years ago, i sold a good 318 to a guy and he installed it in his Aspen, i knew it was good because i drove the car for 6 months over the winter, it was just a rusty p.o.s.
so i parted it out.
Three months later, he wanted his money back, said the engine was bad because he threw a rod out the side of the block.
He always revved the thing to the moon and drove the crap out of it, i seen him doing it!
I told him to pound sand, and he never got a refund. There was some hard feelings over this for a few years, and he wrecked 2 more engines before he smashed the car up.
Bottom line is:
He came to you, he took a gamble, and the tranny that you sold him obviously did what you said it would.
You didn't lie about anything.
Tell him to pound sand........