I would have thought that the royalties to be collected are stipulated in the contracts and are a percantage of the new record sales and a set amount for each record play on the radio. i think this is also covered in the licence fee for clubs and shops that are paid to the BPI. for playing music in your premises, not certain of this. My cousin used to work for the BPI and they used to recover royalties for artist who joined the BPI if you were a member they monitor all adverts and radio's playlist to make sure you are paid.
Do not think it would be viable to get royalties from second hand record sales, as in all things some prices go up and down, how would you monitor it as well second hand sales from 10p to several hundreds of pounds if not thousands. this would then have a knock on effect to the second hand book sales would'nt it, affecting charity shops and second hand book collectors as they would have to pay royalties on books or records sold,
just my thoughts
mark