Their slick salespeople, tv and radio ads promise a lot and play on the hopes of honest, trusting individuals. Then they will ask for upfront money and continually demand more. Here's how it works:
They'll draw you in by sending you a free packet and form (supposedly confidential) for you to return describing your invention. Never send anything to anyone until they sign your confidentiality agreement--not theirs!
They call you right away saying, "your invention is incredible, one of the best we've seen". They say that to everyone.
They'll ask you for $800 to $1000 for a preliminary market study, which may include a brief patent search. It's a boilerplate report, virtually identical for all submissions with a few word changes. It's completely bogus. The report does not qualify how many people may purchase your invention, only how many people might have or use a similar product. Heck, you can find that out on the internet for free in the next ten minutes or so.
They'll continue telling you about the incredible potential [based on their bogus market report] and ask you for more money (from $3000 to $30,000+) for product development, design and patents. You'll get some slick looking drawings done by an incompetant engineer with no experience in the trade. The truth is, if the so-called designer was good at what he does, he'd be working for a top company, not a scam company.
They'll offer to finance your investment at low interest rates and they'll sue you if you don't pay!
When a salesperson realizes you aren't going to "send more money", you'll never hear from him again.
Sadly, you can do all the above yourself for a fraction of the cost, in a fraction of the time, with far superior results.