If you don’t think honesty works in advertising, try exaggerating your product for a while. Make some false promises, show your customers that they’re being used (and it’s really all about you), and see how hard you have to fight for each customer.
Now try the opposite. Try being generous and watch the groundswell of goodwill, as you show your customers that you care about them through your ads and through what you do.
Pretty soon, you’ll start seeing how easy each sale seems to be when you’re offering value and then showing people honesty and the respect that honesty implies.