I'm not sure there is as much profit in it as you think. The most salvageable modular packs are in the S/X, but those make up a small minority of the overall Tesla population. The 3/Y pack is far less modular and the price for a refurb from Tesla is only $12k-$16k, so people would balk at going to a third party unless the prices are substantially less (including shipping) which reduces profits, especially if you expect the shop to charge "reasonable money".
Keep in mind there are overhead costs for maintaining a shop, getting the right equipment, and training the technicians. The few shops dedicated to this will likely charge a higher premium to cover for this and get a return on their investment.