The supervisor took hold of the bag, looked at it. Then said 'I don't know. Free'.

That might be less customer service and more employer disservice.

Case in point: I used to work at a store that sold, amongst other things, role-playing games. One particular publisher, West End Games, never printed a price on their products. Ever. Even in the UPC translation. Despite this, and despite the fact that he wouldn't allow anyone else to unpack the games shipments, my boss, who was also owner of the store, would never put a price sticker on them. Ever.

So when a customer would come to me and ask how much they were, I'd usually make up a price that was somewhere in the neighborhood of what I figured half-price would be.

This sort of thing also happened frequently with Games Workshop games, which were exclusively priced in UK Pounds.

So don't assume that a clerk is being nice to you. Assume he's being bitchy to his employer.