One way to figure out what a patent is worth when it is licensed is to do some sort of calculation of:
1. the expected cash flow from the patent
2. the expected growth rate of the cash flow
3. the risk of the cash flow and growth estimates being wrong
4. and the length of time the cash flow is expected to be recieved
The less the inventor has defined these factors, the greater the uncertainly and the less a potential licensee would likely pay. Some patents are for sale on ebay which basically say "I have a patent, and I think its worth $23,000,000, so that is where the bidding will start." What the inventor has to communicate is why the investor would be better off putting his $23M into this patent rather than somewhere else, like the stock market. Most people who have $23M first of all don't want to lose it, and second, they want to turn it into $50M! Unless the inventor can show how that $50M is going to happen in a rather certain and rapid way, the licensee would be crazy to drop his money into a venture with high risk.