Sold 47re, new owner says no good

So I took a good known 47re out of a buddies truck. It sat in my shop for 2 months, sold it locally to a kid. He had a shop install it and they are saying it won't move an inch. I HATE situations like this!

Mechanic says he didn't even drop the pan and install a new filter. Sounds like a genius so far.



Any ideas what he could have not done right? I just can't see this trans not doing anything. It ran perfect.