Please help with fraud quick with Second hand ram

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I had old two 4gb Ram DDR3 from from not working CPU. I know that cpu had some thermal trip error that’s why it stopped working
But There was nothing wrong with those two RAM that I am very much sure.
Now I sold it to a person.
He did some checking in his old HP computer.
Some kind of RAM counting was happening
And it was showing in the BIOS. Also My rams were indeed getting detected properly.
But his computer were not booting up. Giving some windows crash after loading screen. Maybe some OS issue.
Still he bought the ram from me saying it seems working.
Now one day later he says memory cores are damaged that why system wasn’t booting.
I want to ask is that real thing ?
or he is just messing with me so that I would give him ram for free because he told me its working?
If I give him refund, and is there any possibility that he may have done some kind of locking with ram for temporary shutdown?
So that it won’t work with my computer either?
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