...you could at least make it worth his while by buying from him?
So, a salesperson is polite and patient enough to spend half an hour of his evening, when he would normally be on his way home to his family, which you can tell he has as he wears a wedding ring and has photos of his children on his desk. He is kind and careful and generous with his time. You drag the transaction on and on and on. And then you just say 'oh, I don't think we will buy after all'! So the poor salesman has just wasted half an hour of his pitifully short evening with his family and got bloody jackshit out of it!
Please don't do this to salesmen! Far too many people do and it's not fair. If you're genuinely going to buy something, then fair enough. But if you're not, then please don't make them stay behind after the place closes.