seaming Simple Data Requests are not always so simple

Ever been asked to pull data that seems to be simple.  For example what Repeat Customers do we have.  Only to find out that this simple idea is not so easy when it comes to determining this from data.

This article describes three potential way to pull Repeat Customers using Micorsoft's Power BI component called PowerPivot.

http://www.powerpivotpro.com/2014/12/repeat-customers-in-dax-three-flavors/

What seeming simple request to always get?

Do you have a cool solution for this issue?

If not can anyone help?