value traffic vs. no value traffic.

I am using the Google Keyword Tool to investigate popularity of a potential niche. But there is something that I am having a hard time to quantify.

There are two types of users on the web.

1) ones that are willing/able to purchase from the internet.
2) ones that are not willing/able to purchase from the internet.


I am guessing, but have not found, that there exists a number that indicates what percentage of internet users belong in group (1) across the whole internet.

But what would be more important is to know what percent of internet users belong to group (1) for a particular niche.

Without knowing what percent of users belong to group (1) then Google Keyword Tool looses a lot of its value. Let's say that Google Keyword Tool indicates that the keywords "I have absolutely no money" have 100,000 searches a month. So one would assume that good traffic would result from this niche. The problem is that they belong to group (2).

Do you have any suggestions on how to determine the percentage of people that belong to group (1) for a given keyword search. All I can think of it "use your gut", but I am hoping there is a more quantitive way.