There are basically only three risks to worry about when using an invention submission service for developing your invention, your time, money and your invention. Now that sounds pretty harsh, but it's a fact that the majority of people who go this route never make money with their invention for one reason or another.

There are different type of invention development outfits, some better than others. Stay away from invention development firms that advertise on TV and the radio. These places are known to be utter frauds, and have absolutely no intention of helping you to succeed with your invention.

There are many in the inventor and IP community who have been speaking out against the scams that do exist in the invention development realm. You can read some of these articles at the links below:

RJ Riley's Invention Promotion News Page
Riley's Invention Promotion News

The FTC site about invention promotion scams:
FTC's site about Invention Promotion Scams

Stephen M. Nippers Blog about independant inventors, and invention promotion scams
Invent Blog's Invention Promotion Scams

PHOSITA's Caveat emptor! Invention Promotion Companies
PHOSITA's Caveat emptor! (Let the buyer beware)

You can also read a recent article I wrote about them called:

Invention Promotion Scams

My best advice to you would be, make sure you have documented the full disclosure of your invention in your inventor's notebook. Prototype it yourself if you can, or have someone else make a working model for you if you can afford it. Perhaps file a disclosure document with the USPTO, or even a patent application if you are able to afford it. These all may seem like daunting tasks, however they are the only sure way to continue the development of your invention, and they are all definite progress in the right direction. If you choose the wrong invention development firm, you could be set back years, even permenantly. These fellows particularly love to feed off of the good will and hopes of their clients, this makes them rich, and the inventor heart broken and left with nothing, a bunch of lousy, expensive, but utterly useless charts etc. A prototype has acertainable value, as does a patent. Charts and graphs of product and market analysis are useful in the right context, but can be obtained legitimately without these firms assistance for a fraction of the price.

I am sorry I don't have a better answer for you. I might be able to offer you a ray of hope however. I am currently starting a manufacturing company founded upon some of my own inventions, and I am planning to quickly begin producing other inventor's products as well. It is my intent to license the invention from the inventor, and pay them a fair royalty per unit with a minimum annual sales volume, and the standard gambit of payments which an inventor should expect to recieve. This company (I'm hoping) will be online very soon, perhaps within the next few months.