Jacek's comment also shows something I've been thinking about for a while:

In the beginning, for me the rule of thumb for most of the cards was "rental fee below 4-5% ROI is ok", right now it's more like "rental fee below 2-3% ROI is ok".

This is kind of nonsensical. The owner's ROI has nothing whatsoever to do with the renter's profitability, and I continually see people treating it as if it does, making rental judgments on the listed ROI rather than anything meaningful. It would be nice to have a number here that actually meant something to the potential renter.