My first thought is that they'll ask you to do it for a commission, so you'd earn a percent of actual sales. I'm guessing this because it's unlikely that they can afford your hourly rate for that kind of business venture. Doing sales on spec is a good challenge if you're up for it - and potentially pretty lucrative. If you trust your skill as a salesperson, and really like the product, it may be worth the risk.

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Mary H. Ruth/Virtual Writing & Communications
http://www.writingVA.com