If he feels he still has rights to the rental and the deposit, then that also means he has responsibilities for the damage and is subject to charges.

If you're looking to treat this as a regular rental, then charging undermarket rent throws a monkey wrench in that. 

I do direct booking through the Houfy website, taking credit card payment by Square. 

Or, you could ask for a rate quote based on a range of credit scores and you can figure out what they'd charge you on your own.

Those two factors work in you advantage allowing you to charge rents that let you cashflow when others trying to get in the market couldn't purchase a similar house and make the numbers work. 

The one I worked with and fired in Jacksonville charged 8%.

If you play your cards right, this could be a great way to build equity and add value to the property.

I also have a friend who is in development for renewable energy; solar and EV charging stations.

But I think you could take this a step further and instead of charging no rent, your rent could be the cost of the taxes and insurance annually.

You can't charge extra pet rent or even a pet deposit because it's legally not considered a pet.