t sounds like a retailer may have to pay some VAT on the goods they purchase for resale and then that need to be able to offset what they have already paid vs what they collect from the customer.
(Am I guessing correctly?)
Generally in the US we file as tax exempt and then pay the taxes on any goods we consume.
My wife (for example) pays sales tax of List price and then if she sells anything at a discount she needs to request a refund of the difference.
You are being very helpful
tom