What guarantee do you have that your idea won't be stolen if you tell someone about it? So that your idea won't be stolen, you need to first apply for a patent. But the process could kill you than if you share your idea with someone, who must have the financial capability to convert your idea into something that will benefit humanity and the animal kingdom. Just kidding.
Sorry, but you should have not used the word, "sell," because ideas can not be sold other than thru a patent or if it is made into a product or service...Apart from these two, you can not sell ideas - you simply "share" them, making use of that famous instrument called, NDA, if you so desire.
Still, there are people who can be trusted; who can help you refine your idea and formulate strategies. Some of them gladly offer their talent for free - though not for long...:p If you want solid, lasting results, you must hire or work with not only competent individuals; but those who give you that "warm, fuzzy feeling" that you hope your customers will also feel when they come to your business...You must make way to work with these people through an arrangement they can't resist, or that will benefit both parties even if it does not involved financial compensation at the start. You just have to convince them.
Just my two cents....You can tell me your idea if you want. :)