I came across a 2-flat with a basement that has been converted into garden unit with 3 bedrooms and kitchen and bath.

This could be a flat fee or a percentage of their assignment fee.

I do have a nightly pet fee but i put in my listing that if someone is bringing a pet for an extended period of time they can also reach out to me to discuss a flat pet rate for their stay.

That was a year ago with debt mounting higher & income flat if not  lost.

But there are things you need to consider, like: everyone has to follow house rules to avoid drama, excessive use of kitchen and bathrooms leading to plumbing issues, being on call 24/7 with any problems, etc.

I will just have my bookkeeper bill a flat amount monthly from Jan 1st on. 

I came across a 2-flat with a basement that has been converted into garden unit with 3 bedrooms and kitchen and bath.

wow never seen flat roof designs in that part of the country. 

Flat Fee buyer agency to reduce acquisition costs (get ~2% of the sales price back), and flat fee MLS listing to reduce selling costs to ~$500.

No excessive fees upfront or during holding period4.