If you don't do it with excellence, don't do it at all! Because if it's not excellent, it won't be profitable or fun, and if you're not in business for fun or profit, what the hell are you doing there?
Never write an advertisement which you wouldn't want your own family to read. You wouldn't tell lies to your own wife. Don't tell them to mine. Do as you would be done by. If you tell lies about a product, you will be found out -- either by the Government, which will prosecute you, or by the consumer, who will punish you by not buying your product a second time. Good products can be sold by honest advertising. If you don't think the product is good, you have no business to be advertising it.