I sold a pair of tefillin written by a well known “reliable” sofer. It turned out that it was pasul because he wasn’t writing it by hand rather by computer & touching it up in a way that it was almost impossible to notice. Am I legally responsible to refund the money to the buyer? I won’t be able to go back to the sofer & get my money because he doesn’t have the money to give refunds even if he wanted to.
You are responsible for refunding the buyer.
Although you made the mistake in “good faith,” and you were unaware of the fact the tefillin were pasul, the fact remains that the buyer meant to buy kosher parshios, and he received pasuk ones. Therefore, the sale is void (if the buyer insists on his rights), and you will have to refund the money.
In principle, you can of course claim your money back from the person who sold you the parshios. As you note, this is unlikely to help.
It is troubling to hear that such frauds are present in the Torah community.