Would you do this if it was potentially worth $100,000?

And no, i'm not talking about pimping out your body, so get your minds out of the gutter

Anyway here's the deal. I have been approached by a client who is after some very special web development services. I have given him a development price for the project, and the client has returned with a percentage based payment, sort of like a partnership. This percentage payment is potentially worth $100,000 over the period of the project.

There are problems with this form of payment. The project has to succeed in order to pay me at the maximum potential. I am at the mercy of someone else's marketing strategy and could possibly get a percentage of nothing if the project failed, and that would mean no payment for the project at all.

Anyway, I have asked the client several questions at this stage. Because this is looking like a partnership I need to review the business plan, project plan and marketing strategies for the entire project. I will also need to get legal advice on this to cover my butt.

What would you do, would you take on a project at this level simply because of the high potential return? Would you state that you only work for fixed quotes or a fixed hourly rate? Would you ask the client anything else? What would be the deciding factors for you taking on a project like this? Remember there is potentially a huge reward from this, it is also very high risk and I could get nothing.

PS. I am not letting anyone in on this projects concept as I keep strict client confidentiality. So please don't ask what this is for, just think about what you would do if someone asked you to build a site and they would pay you a percentage return for payment.