Network Q Haggling?

[Trevelyan]

I'm on the point of buying a used Vauxhall through Network Q at a dealer. It's been a good few years since I bought a car like this, my last couple have been new cars bought through a discount scheme where the price was fixed. I'm whether to try haggling on price (something I'm not particularly comfortable doing) and if so how much to aim for.

Has anyone who's bought through Network Q got any advice? Are the dealers generally prepared to negotiate on price?