Know Who Buys Again.

What it is

Kevin Hillstrom runs MineThatData, a consultancy, and has written its blog since the 2000s. His first book, Hillstrom’s Database Marketing: A Master’s Complete Method for Success, came out in 2006, followed by books on multichannel and merchandise forensics.

The theme across all of it: the customer file is the business. Read it closely enough and it tells you who buys again, who’s drifting, and whether your marketing did anything at all.

What we took from it

Define value by what customers do next. His working definition of a loyal buyer is a probability, not a feeling:

“I define a loyal buyer as somebody who has a 60% or greater chance of buying again in the next year.” MineThatData blog, October 20, 2026

And test honestly. In 2008 he published the data from an email test on 64,000 customers who’d bought in the past year, split at random into thirds: one got a men’s email, one a women’s email, and one got nothing, and everyone was tracked for two weeks. Comparing each email group with the group that got nothing shows what the email actually changed, rather than who was going to buy anyway. The dataset is now a standard example for teaching uplift modeling. On testing in general, he put it this way recently:

“A/B tests are humbling. They force you to address your personal marketing belief system.” MineThatData blog, October 21, 2026

Where it shows up in our work

Two habits we use every week. Judge customers by what they’ll be worth, which starts with whether they buy again. And judge marketing against a holdout, so a campaign gets credit only for the buyers it actually moved.