I have heard of this before. I even met someone who claimed they they would do this with their high cash back cards and claimed to reap thousands in rewards with unlimited cash back. Even said they would open new cards to do this with they high dollar promo periods and high credit limits and would just do this while the promotion was active.

Claimed to have made thousands on it, maybe even 10s of thousands

I always wondered if your credit scorn would be all jacked because it would report this high to zero usage