I replied to a post the other day asking basically the same question, here was my response.
I've been monetizing purchased data(email) using PPL (pay per lead) offers for over 16 years.
With PPL there is no credit card required to complete an offer...no purchase needed. All a user has to do is fill out a form in order to generate a commission. So conversion rates are typically much higher than those requiring a sale. I will also promote other types of CPA offers, but I will use them on the back-end and use PPL on the front-end, since they are basically free offers, but still pay well...offers the path of least resistance to getting conversions/$$$.
I generate traffic by acquiring fresh / targeted data that I know what the users are interested in and that a PPL offer exists that matches their interest. I generate real-time co-reg that targets specific PPL offers. I also work with aged data, but this is a bit more involved and required some additional resources and tools.
This way I'm building assets that I then own and can market to over and over...I own the traffic. Compared to what most marketers do, which is to always be paying for traffic, which typically results in a bunch of clicks and then can't market additional offers to.
Anytime you buy data, it will never be as responsive as list(s) you built yourself. So you have to work with high volume to compensate for it, but this is fine, because it much cheaper and faster than building your own list(s). The key is that when you mail, you always need to be collecting your opens/clickers, so that your segment the most responsive user into smaller, but very responsive list(s). Then you will be sending less and making more with each mailing.
There's obviously much more that goes into it, but it really does work and can be extremely profitable. Everyone that I know that is in the business and knows what they are doing, does 6-7 figures. While that may be a huge range, a lot comes down to ones ability to scale and effectively manage the infrastructure that goes into scaling.
However, it's not for everyone. It's really a business model and it's far more costly to start up than most CPA strategies that only cost a few hundred dollars. Data, tools, resources, etc, etc... it all adds up.
Anyway, something to think about.