Warranty policy on A, B, C graded items

Hi, I would like to know what the faulty returns policy is regarding item grades. For simplicity, let's assume the fault is entirely internal and the store agrees the customer is blameless.

1. If you bring back an item that was bought as grade A and is still grade A, can it only be replaced with a grade A?

2. If you bring back an item that was bought as grade A, but now has cosmetic wear, would you have to accept a B or C replacement, potentially with other customers' sweat/fluids/earwax included?

3. If you bring back an item that was bought as grade A, but would now be classed a C and there are no replacements available, would the refund amount be based on the C grade price?

4. If you bought an item that was an amazing grade C (e.g. it was pristine but had an engraving), would you have to accept a heavily scratched item with burn-in, non-original parts, a dying battery and missing accessories as a replacement?

I'd also be interested to know if there is an official policy on this or if managers generally make up their own rules. Perhaps it is all dealt with on a case-by-case basis?