I went into Best Buy a while back, and spent ~45 minutes with an associate discussing cheap cell phones for plugging sim cards into while going overseas. He ended up recommending a phone they didn’t have, and I ended up extremely satisfied but also buying it off the internet.
I asked a manager if I could give them 5 dollars for their time and excellent assistance. Got a fairly strange look, and a “no, just buy something or come back?”. I didn’t want to buy something, I will come back; but I also wanted to give them *something* right then.
It seems like it would be super easy to set up a “service donation box” or whatever you want to call it. Maybe the logistics is more effort than its worth, but that sounds really unlikely. And a default position of “absolutely no need or pressure, its just there if you feel like compensating us for the service you received” or whatever would eliminate most bad publicity/greedy feelings.
This is particularly relevant for Best Buy and other places paying for knowledgeable staff and floor space for displays so you can physically try out products. But really could apply anywhere.