We offer a guarantee that we can provide you with a statistically significant increase in revenue in 60 days or less or we don't get paid until we do.
For those who aren't statisticians, statistical significance is based on several variables, but it's designed to hold us accountable for our results. A test will be statistically significant if you were to repeat the same exact test then the likelihood of achieving the same result would be 90% or higher.
A lot of things have to happen for a test to be "significant", but the important thing to keep in mind is that a $1 increase in revenue wouldn't be considered "significant" under any testing parameters.
So, you are not being taken advantage of by the wording of this guarantee. It's legit, and it has your success first and foremost. We do this because we're 1) extremely confident in our abilities, and 2) we want the burden of risk to be on us, not you.