I guess that depends on what exactly you consider as “low to medium.” If at the cash register they ask whether any of the staff helped you with the purchase, it’s likely that they get a commission for it. At least where I live, that will normally be the case in places where you can get someone to help you seriously.
On the low to medium end it seems logistically impossible for there to be a link given the way they set up the store.
I guess that depends on what exactly you consider as “low to medium.” If at the cash register they ask whether any of the staff helped you with the purchase, it’s likely that they get a commission for it. At least where I live, that will normally be the case in places where you can get someone to help you seriously.
(A typical example of such a store is J. Crew.)