It's against the law yes, but it's very hard to know if it is happening etc. I've no idea if anyone has actually been caught and prosecuted and what sort of fine they received.
Its up to the Shop which the person attemped to buy one from i guess even so as long as he didnt walk out the shop with a RiF he can only be told about the law
however i the shop sells him the RiF its more there fault then the buyer because the buyer might not know about the law but the shop must if there selling RiFs so it would be the shop getting in trouble more then the buyer
We have rules that the seller must check the buyers defence, obviously if I was to find out that this had not taken place then I would take the necessary measures to stop the sale and report it. You can see the rules we use if you go into a sale section and look at the 'Read First' thread.