Legal Aid, Sentencing and Punishment of Offenders Bill

Can the Minister clarify Section 3(1)(a) of the Scrap Metal Dealers Act 1964? It seems a bit odd that the only condition required of these people is that they, "““obtain from the purchaser a receipt showing the weight of … scrap metal comprised in the sale””." We have all had receipts from people for getting things like that, probably without even a piece of carbon paper between the two. Why is it necessary to give such people an exemption when the only condition I see here is that they get a scrappy piece of paper as a receipt? It seems to be left wide open to shove things in a container and send them off to China without any paperwork at all.