I never give donations at checkout. I do my charitable giving directly, I don't want a middleman.

What makes me less likely to return is the number of questions I get when I'm just trying to engage in a simple exchange for goods or services. More than one, and I definitely think less of the business. No questions definitely makes me think more positively of the business.

I rather thought I was the only one (within a rounding error), but perhaps not.