Before choosing a keyword, i want to know whether there are advertisers for it or not. How can i check that? Does number of advertisers effect the paying tendency of a keyword? How do i know about the paying potential of any keyword?
Before selecting keywords always use Google Keyword Generator Tool. Compare the keywords by checking Globally and locally monthly searches for that keyword. Then decide which one will suite for your website.
Yes, number of advertisers does effect the paying tendency of a keyword. And you can check from a competition bar that how many advertisers are available for that specific keyword.
In addition to that tool, I would suggest looking at the number of sites in google for the keywords, but globally and within the last week to get a better feel for the usability of that keyword.
For Advertisers analysis, you can use the metrics of competition in google adwords keywords tool. Or you can go for spyfu.com, semrush.com and keywordspy.com...
http://forums.digitalpoint.com/showthread.php?t=2224078#post16477919, hope you will get some thing better in here.