Some of the the best buyer keywords are those where people have been paying consistently to advertise. The way i see it, they wouldn't be paying for advertisements if the ads weren't having some form of ROI right?
Started using SEMrush.com recently and this is what i do:
1) Type in a keyword i think is a buyer keyword worth going for and make a note of the top 10 domains ranking on page 1.
2) Plug the domains in the backend at SEMRush.
3) Look in the Advertising Research (particularly Ads History section) for keywords being advertised the longest. Typically keywords that don't have any month gaps in them in the Ads history section are worth looking at.
4) Make a list of keywords in an excel file.
That's how i go about it. You can also cross reference the keywords you get from 4) with keywordspy.com and spyfu.com as well :-)
If you're going the "product launch route" the typical ones are where the money's at e.g:
PRODUCT NAME PRODUCT OWNER e.g. article builder jon leger
PRODUCT OWNER PRODUCT NAME e.g. jon leger article builder