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HMRC internal manual

VAT Refunds

Unjust enrichment: Some items to consider: Pricing / margin

You should examine the period of the claim then look back through the trader’s records to see if the price has increased at all. 

If the price went up when VAT was added, we ought to be able to show that the VAT charge was passed on. However, if the price has remained the same this may be more difficult.

We need to know the average margin the trader hopes to achieve. It would be useful to consider overall margins achieved in that particular market sector.

If the trader is making lower margins than is generally accepted for a given product, it would probably be difficult to prove unjust enrichment. The claimant might reasonably argue that, by incorrectly accounting for VAT, he has suffered a loss of profits.