Re: "and it's obviously not illegal"
He'll find out if it is illegal (or not)when he is woken up at 04:00 one morning when HMRC force entry to his house and get thir missing VAT back with interest.
IMHO, HMRC should start surcharging Amazon and EBAY for the unpaid VAT. They'll either come into line or quit the country.
Biting the hand that feeds IT
