Fuck all.
Don’t waste your time negotiating because whatever you say over the phone isn’t good enough for these type of people & they always want it for less - most don’t have anything approaching sensible money anyway. Even if you allowed them to rape you most of these bottom dollar twats would then want to rape your Mrs/partner/lover (delete as appropriate ).
Depending on how the punter sounds & how direct I feel the need to be, my response is a variation on this;
That’s the price, It’s freshly MOTed, described correctly, xxxx service history & honestly videoed. If that price isn’t good enough there’s plenty of rubbish out there with 3 months MOT, knackered tyres & brakes. I’m doing the job right, if you want to buy shit to transport your family then go & do so.