I managed an AutoZone store for awhile, and employees got a 25% discount; the mentality their upper management has tells me that was of little concern to them.
Name-brand US-made or offshore origin, same deal.
Wouldn't surprise me if their mark-up was 100%; they have to eat a lot of stuff when Customers buy the wrong part, try to hammer it in, then return for the full refund.
AZ returns those to the manufacturer and they end up eating that expense instead of AZ..."cost of doing business".
Storefronts are expensive to build, operate, and staff, plus the advertising/promotion, loaner tools, and there are several layers (seemed at least 3) of management.
The cost for plowing snow one month was around $1,200, but that was a pretty heavy winter.
A buddy of mine who makes tools sells directly to Summit, Jeg's, Speedway, etc, but IIRC Summit's stuff mainly comes from/through A-Tech; maybe Jeg's & etc, too.
He actually makes a bigger % than they do, but he buys mostly offshore and does his own assembly, quality control/testing, and some packaging.
IIRC, the stuff retails at about 75 - 100% markup above what he gets.