Haggling over anything anywhere comes down to the same basic premise - if the seller is not making the profit margin they want, they won't sell.
That applies when buying tablecloths in Spanish markets, they may grumble and swear at you in Spanish, but if they sell, they are making money, if not, they refuse.
So offer a lower price, and be prepared to up ot to a level you have set for yourself. Depending how keen they are to sell, they will meet your price, or not. If not, smile and walk out. If they don't follow you outside to try again, they are confident of selling at the price offered to someone else.
You have to decde how much you want this car, and how much youi are willing to pay for it. Armed with that info, in you go and see what happens.
Don't be 'British' about not hurting the guy's feelings - they are salesmen, they leave their feelings at home when they come to work!