Lost VAT revenue is not due to mom-and-pop shops offering a discount under the table. The vast majority of lost VAT revenue is due to organized VAT carousel frauds, also knows as missing trader fraud, where an organized groups of 10-20 people siphons tens of millions into their pockets through reimbursements of fictitious trades. It's one of the most lucrative fraud schemes there is, but if caught and convicted, the sentences are usually comparable to that of murderers. If not caught, the accomplices frequently try to assassinate each other in a sort of a sick tournament-style elimination