Could of Come From king Richerd's Horse ... Bosworth pillaged

This buckle, apparently from the Battle of Bosworth site is from the ‘Let’s Go Digging’ Facebook site. They pay farmers for the use of their land and finders keep anything below £500, though share treasure rewards with the landowner. They sell finds on the site, seems to be a common occurrence these days. But of course they are 'only from the ploughsoil' (Ixelles Six academics), 'so it does not matter'. Eh?

The finder says:

For Sale ......
Found back in my early detecting days.  Now a very RARE collectors artefact.
* Towton Battlefield land now has metal detecting ban restrictions imposed by The Battlefield Trust and landowners. * LARGE Military Horse Buckle find from the Battle of Bosworth Battlefield fought in 1485. Very good condition with intact pin. FREE Postage included - signed for. PayPal or Cheque  ........ £39

Note, what he is selling is a provenance. It does not seem to be in the PAS database, if not, the artefact hunter and buyer are guilty of knowledge theft. Is the 39 quid going to be split with the landowner?