Skip the bullshit. Tell your customers exactly what they're buying. If it's what they want, and it's any good, they'll buy it. And they'll respect you for it.
Don't be afraid to talk about your shortcomings. The customer will find out sooner or later anyway, and if they know in advance, they won't badmouth you later.
Don't try and bamboozle the customer. Sell what you're selling. Don't waste your time and theirs promising them one thing and then trying to persuade them they wanted something else.
Sincerity. When you can fake that, you've got it made.George Burns