I'm certain this will come as a shock, but I sold cars for a while. I was quite good at it; I was able to be assertive without being aggressive, friendly without being over-eager, etc. The hours were hell though, so I did something else.

Anyway you've got the right approach to it. And it is a skill, very few people learn it naturally. Sales and self-promotion are intertwined, because as any good salesman can tell you, the product (provided it is a good one) isn't all that important. It is the relationship that you can build with the customer, the rapport you can create. You have to convince them they can trust you on making that decision. And, of course, you need to be worthy of that trust. Good luck with it and I hope you find exactly the sort of job you want.