If you're negotiating contracts and using potential sales of a given product as a make or break metric for the deal you're doing it wrong. Sales potential of a deal is absolutely not the most important fact. That's get the deal went through anyway.
Sales potential is just that, potential, it actually means nothing, it has no value, zero. Signing a deal though, that's where the money is. That's a quantifiable goal that has to be met before any sales happen. It's far more important to get into your target market, afterward you can address product velocity issues. Products can be changed to suit the need. Deals are fairly static.
It's just like job interviews. How many times have you said 'you know you can get the job, if you can just get the interview'? Get the interview first. Once you've landed the job you can do whatever needs to be done to make sure your performance is satisfactory.