I have trained many people how to sell, but I believe that is different than a natural ability. I will rarely buy something when the salesperson is pushing me. If I am walking through a mall and someone wants me to sample their product or service, I will smile and walk quickly away. Personally, I don't look at that as selling but plain obnoxious.
If you are interested in a humorous look on how NOT to sell, I wrote a blog post about it a few months ago called 10 Ways To Guarantee You Do NOT Make A Sale. Have a look here to get some valid tips on what NOT to do.