And on the other hand. This guy could be onto the next big thing. And you guys have just written off, and you'll never know what you might have written of, becuase his approach was a little non standard.
If I followed everyone else's dreams, I would be dismissing my own. This may or may not be the next big thing, but statistically, it is a VERY long shot. Let's say it is the next big thing, how do I know that I will ever see any value? What is 10% even? Do I have access to the books and able to audit the value? Am I part of the negotiations to sell the business? At 10% ownership, I doubt it.
Now, I am left with someone that I don't know having total control over the financial outcome of this (likely) dubious effort. Like others here, I have dealt with all types of business people and the thing I learned is that you only trust those that have earned your trust. Blind trust is not how you get things done. With that said, the initial pitch is not worth any consideration since it requires trust as the first step followed by a totally unknown and proportionally small percentage.
I am not even close to being gods gift to engineering, but I can (and do) make a good living with only 10% of my ideas actually getting any business traction. This is similar to what VC's expect - 10% of their investments make 100% of their returns. 90% fail completely as a total loss. With that as my business model, I am in a great spot. This offer is required to be 100% successful with a single idea. Just that on it's own is enough to move on. The OP may have great intentions, but I have no motivation to bother when I can do my own thing and have ZERO worry about anyone else that can sour the deal.
Now, if a savvy startup group came in and offered a roughed-in contract with a signing bonus and guaranteed R&D budget - plus 10% - I would at least listen. That would show that they have taken the time to build a plan/team/projections and have already taken real risk. Subtract all that and I want a starting offer of 50% just to get me to the table. I already know how to prosecute a variety of businesses from concept to sale - done it. I already know how to design, engineer, and manufacture a wide variety of products. I have done marketing, trade-shows, press releases, web-site,web store, etc. With all that on the table, this is still an uphill battle.
If the OP is looking for less experience, then the uphill battle starts to look like a vertical, jagged cliff, 3000ft high. For 10%, I would expect someone to step forward that has (maybe) one piece of a complex skill set needed to get from a napkin drawing to a store shelf. To get the whole project done you either need a team or you need one very widely skilled and experienced individual. Widely skilled and experienced individuals don't need this kind of offer. Their experience and skills offer much more and better opportunity.
The OP writes about how negative this bunch is......don't confuse negative people with realistic people. Take a look at your offer and your pitch technique. You are asking for high-end, offering low-end and doing it like an 8th grade science fair project. That is constructive criticism that you should at least consider. When you are asking for money, you better be a pro. Have data, details, risk assessments, payout scenarios - anything at all.
Also, keep in mind, a forum like this is like any social gathering. We are all standing around have various conversations and this random, unknown person walks in and dives right into a pitch. In a real life social situation, this would get many blank stares, followed by "Who is this guy?". Don't start with the pitch. You look, sound, and feel like a pitchman. No one likes to be ambushed by a pitchman regardless of what is being pitched.