Some mechanical parts I would not shy away from used.
A torque converter on the other hand, I would not buy because you have no idea of the condition of the trans it came out of. You could end up contaminating yours.
I will back you up on the converter comment.Bought one off other site but the seller now sells here.Nowhere performed like advertised.Took to converter shop went to dumpster.$250.00 out the door.