To determine a domain's most profitable (paid) keywords we look at habits like how much they spend on these keywords, how long they have been buying them, how consistently they buy them, how much they have to fight off competition, and how much attention they give to testing and improving ad copy for them....
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Over time, these habits correlated with profitable keywords so well that we felt this was a confident method.

True profitability for the domain will come down to how well they convert on their landing page and how their products/services are priced, etc. However, in the big picture of competitive research, advertisers get a huge boost in learning which keywords their competitors rely on the most.