Inventions- anyone ever successfuly dealt with one of those invention firms?

From experience, I'll give you this..........
A good place to start is looking for local inventors groups, they usually have monthly meetings, and you will learn alot. Put an ad on your local Craigslist Gigs or search Craigslist for a Company, (factory). If your idea is plactic, then Plastic injection molding company. If metal, then metal stamping. If your idea is good the factory may manufacture it for the rights to be the manufacturer. Same thing for the inital design drawing, you need someone that does CAD DESIGN, Craigslist always has them that freelance for a fraction of the cost. Suprisingly, once your CAD Design is done you can get a real prototype for about $600.00, (depending on how complex your idea is) Patent....don't worry, go to the USPTO website and get the form for a Provisional Patent, cost $80 and you file it, and you basically have a year from that date to file for a real patent.
The main thing is those companies will end up using up valuable rescources and give you very little to get your idea off the ground.
I did it, and it's been a long road, I invented a very simple plastic product......paid a little money here, and a little there over the course of about six years. Most everyone involved accepted payment plans I could afford, even the Patent attorney. I think total investment was about $15-20K, which I've made back through selling my product. Your biggest obstacle besides getting it off the grounf=d will be getting it out there, Marketing it.
If you need any feedback on your project feel free to contact me, I brought an idea to market.
 


One note on the marketing, distribution. Nowadays you have the internet for marketing, you can make a website, a blog, sell it on ebay, amazon. Basically you can market it yourself. Here's your real advantage- With the marketing skills I see on this site you could make a marketing campaign that one of those "Companies" would charge you thousands and thousands of dollars for, and would be ten times better.
I'm at that point now.....I'm trying to learn about "affiliate campaign's" because that might be what I need to increase my products internet presence, but that's a new thread.
 
In the meantime, we had huge competitors coming out with similar products but just enough different. We didn't have the capital to fight the fight back then. Getting a patent is only as good as how well you think you will be able to defend it.

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1st, search to see if your idea is already patented

2nd, if it isn't and if you are not going to create the product yourself but you're going to hire a manufacturer, you need to get them to sign a NDA and non-compete contract.

3rd, keep records from when you conceived the idea, and initially made your prototypes.

4th, once your product is made commercially available to the public and sold, it can no longer be patented, and it is fair game for anyone to create something similar.

Get your game together. Plan your attack to try and dominate the market for your particular product in the first 6 months. (make what you can)