At some point in time, you will get a VAT inspection in the UK - particularly if you are importing. Believe me it doesn't go unnoticed.
Customs & Excise will diligently check your invoices to see how much you purchased a product for. They will compare it to your bank / paypal statement to confirm that you paid the exact amount of the invoice and they will then check that y ou paid the correct amount of duty. My last VAT inspection was about 18 months ago and I am expecting another one soon.
I think that it is something many of ther so-called bedroom sellers on here forget when they are getting goods into the Uk and their supplier is marking down the price. If you don't inform HMRC that there is a discrepancy and pay the extra to them, you are in for a bumpy ride !
It WILL come home to roost - when I see some of the prices that guys are selling at, I KNOW they aren't paying all the VAT/duty they should have.