Parkers is useless as a price guide
Glass's is what you want really, though i've no idea if they do free valuations like Parkers do.
You can get a free glasses valuation through networkqs website.
A dealer will always try and put you on the back foot, if you're haggling, so even if you told him you were using a Glasses or a CAP Black Book he'd probably just go "Nah mate, that's because......"![]()