Very interesting tips. I am a bad seller, was never able to work on anything that involved selling. As a college student, I worked on some selling gigs, but I was really bad at it. I want to think that it had to do with selling bad products and having to present them as high quality ones.
There were these bathroom rugs that i was supposed to sell as sturdy but when you pulled the fibers, even gently, they would stick to your fingers.
Selling involves some manipulation but it is better if at least the products being sold are good enough to make buyers happy.