When the necks on my basses need a trussrod tweak, they're never bowed as heck with a ridiculously high action; they're slighty bowed with a slightly higher action than is optimal.
It sounds like the neck is knackered and the shop owner knows it is knackered.
Here in the UK there would be some comeback if a shop sells a secondhand item that is already broken when sold, but I'm guessing there's no such consumer protection in the land of the free?