The feedback I get from agents and inventors who have negotiated a licensing deal is that the vast majority of corporations deal fairly with inventors. If an inventor were to sue them, a jury would likely characterize the litigation as David vs. Goliath, and be biased toward the inventor. The last few years have exposed corporate behavior that has resulted in widespread mistrust and antipathy toward corporations. Thus, juries may punish those that exhibit even the appearance of mistreatment of inventors.
Take the case of Robert Kearns, the fellow who invented the intermittent electronic-delay windshield wiper. Automobile companies began using Kearns’ invention around 1969, ignoring his patent. Kearns had demonstrated the device to Ford, and Ford contended that to merely apply a well-understood electronic time-delay circuit to the concept that Ford had already developed as a vacuum system didn’t meet the Patent Office requirement of “unobviousness.”
In any event, Kearns collected $10 million from Ford, and $30 million from Chrysler, but eventually lost his suits against GM and Mercedes.
Such precedents have caused corporations to be exceptionally careful about getting into deals with inventors as well as taking advantage of them.
But what about the companies that claim to help inventors develop and license their inventions? These companies operated without much governmental restriction until 1999 when the American Inventors Protection Act was passed. This act requires such companies to disclose the following information to its prospective clients:

The total number of inventions evaluated in the past 5 years, and how many received positive evaluations, and how many received negative evaluations.

The total number of customers who have received licensing agreements as a result of the company’s services.

The total number of inventors who have received more money than the company’s services cost them.

The names and addresses of all previous invention promotion companies with which the present company or its officers have collectively or individually been affiliated in the previous 10 years.

Obviously, these disclosures discourage a large number of would-be clients. But apparently enough inventors really believe that their invention is the exception, and willingly hand over between $10,000 and $15,000 only to find that their widget isn’t one of the approximately one percent that makes more money than is paid to the company.
The percentage of positive evaluations in the first bulleted item should be a clue to every inventor that the company is not providing legitimate preliminary evaluations. Many of my clients have shown me positive evaluations of inventions that are already patented, or are on the market. A search at www.google.com/patents will reveal similar or identical inventions. And by entering the product description in a few different ways, similar or identical products will show up. Any evaluation by one of these companies that is not based on a patent and product search is unconscionable.
In my opinion, any invention promotion company that gives positive evaluations exceeding 20 percent of its submissions is questionable based on what percentage of inventions are commonly understood to make it to the market. The argument that no one can predict which invention will succeed and which won’t is valid to a point. But the blatant overlooking of what’s already been done is not legitimate.