Double Application Fee for Couples?

[Michael S.]

When my wife and I have rented places for ourselves previously, we only ever payed a single application fee. However, the prevailing logic I've researched says that each person over the age of 18 living in the house needs to have a separate application and application fee. 

I just showed a unit to a couple, and the woman was a little surprised that we charged two fees. 

What do you guys do? I know it's hard to hinge on the "couple" criteria since anyone two people could technically be a "couple". Do you guys waive one of the fees (and either not run credit/background on one of the applicants, or eat the cost yourself) when two people come together?