I am sure I am stating the obvious but why not?
1) grab bags are all about trust. You need to trust that the store has put all the hits in there and that they haven't marked the boxes so they give the hot ones out to their friends. Also, you need to know the real odds of getting your money back.
2) sports card shops aren't (intentionally) non-profits. So they aren't giving you amazing odds. Sounds like they are clearing out some inventory.
I have no problem with this as long as you know what you are gambling on.