I had the pleasure of working for them some years ago whilst at uni. The guys on the KnowHow desk were mostly pretty good to be fair, very good at calming irate customers down and helping them.
Returns wise it was a PITA. They used really old software (Because they paid a fortune for it) and the whole thing was not set up well for returns. For a start you had to have special clearance for it, which usually involves getting the manager (Who will try anything to not take it back). Also, they don't work on commission but sales are tracked and you'd still get a berating if you don't meet 'targets'. So if I sold a 3k laptop, that's basically my weekly target right there, if it gets returned, it not only would wipe that out, but then you get questioned to make sure you did everything to make the customer keep the product. The next problem was with actually processing a return, if another salesperson sold a device and I return it on my login, I would get in trouble due to the points above. So you'd need to log into the other persons account which could get ugly in the staff room... All this is why when you try return something, you mostly just get directed to call a Helpdesk, and they'll tell you to take it back to the store.
I was only there a year, I will say most of the staff were pretty decent people. The senior ones are often the ones to avoid. I left on moral reasons, I would just do returns or tell people where to get a product cheaper. Or if they would come into the store in say September this year looking to buy a new MBP, I would tell them they might want to wait until October. And the managers love it when you don't convert stuff to sales the moment a customer walks in, regardless if they come back a month later, because targets people!