[bigjimmyk3]

While reviewing statements from our processor ~8 years ago, I noted that some transactions had slightly higher fees than others. Research found that those were... rewards cards. So, the processor may pass some of the cost along to the merchant.

As for the "free money" argument, research [1] suggests that humans tend to spend more when using credit / debit cards than they do when using cash.

[1] https://www.psychologytoday.com/blog/ulterior-motives/201001...