If you do not want to feed a snake live make sure you ask what they are fed on and only get f/t fed snakes.
Ask when they were born and if getting a morph what the genes are. Ask things like when they last ate, when they last shed if they have and how much they weigh.
Haggling is ok but be reasonable. Offering $50 for a $200 snake isn't a good idea. Don't necessarily take the cheapest seller. If someone is trying to offload a snake because they are afraid they can't get rid of it, you might want to rethink their quality of care in being a breeder and raise a flag on getting such a cheap snake.
If they will not let you handle a snake, do not buy it.
If you don't see what you like for the price you feel fair to spend and from a seller you feel you can trust, don't buy.