I generally just buy if I like the item and price, and can afford it. I seldom try to talk someone down.
Those times though....
Flea market
Don't you want that card?
I do, just not at that price.
Ok, why?
Because I'm a cheap **** (He'd used that language earlier so it was ok)
After a good laugh we talked about collecting for a while, and he offered a decently lower price. I bought the card.
Some flea market guys were a bit pushy. And my standard reply was that I already had whatever they were pushing.
One day I casually mentioned that I was thinking of setting up to sell off some extras. That particular guy was a regular, and very pushy. He had me come to an out of the way part of his setup and handed me a couple boxes of Topps minis, the late 80's ones. They were new and selling pretty well.
Yeah, I don't really want these.
They're free, just don't come set up here for a couple weeks.
Ok then....
Whenever I was a bit broke and wanted cards, I'd just mention selling to him and took my bribe.
Perhaps not my finest moments, but he offered.