Watch List notes:

BRITISH COINS, George III, guinea, 1770, third laur. head r., rev. crowned shield of arms (S.3727), deep scratches from G of GRATIA to bust, surfaces a little dull, otherwise extremely fine, rare
This is one of the rarest dates, and the highest priced in the Standard Catalogue, of the guinea series from 1765 to the 1813 military guinea.

Estimate: £1500-2000