How do I negotiate?

Before buying my car locally, I went to a Mazda dealership near my parents’ house. I had no particularly place in mind to buy the car, so they were a possibility. I told them I wanted to test drive with my parents, and they told me no. If I wasn’t buying right then and there, they didn’t have a sales guy or a car to spare. It didn’t look that busy to me, but hey, I look young. Maybe they thought I was jerking them around? Too bad for them. I’ll certainly never buy a car from that dealer now.