Let's say you're renting a car, and there is a $100 hold that is placed on your credit card for the duration of the rental. If you had the option to pay 9% of the $100 deposit, so $9 upfront to not have the $100 hold placed on your card during the rental, would you pay the non-refunded fee? That would mean during the duration of your rental, you would have access to $91 and wouldn't need to wait days after returning the car to get $100 back.
Consider the same option is available for other services like hotel rentals, Airbnb, apartment security deposit, etc.
Further, credit cards already allow people to get cash advances in an emergency.
Lastly,taking a $91 loan for an interest rate of 9% is financially insane.
I don't know if my repulsion at this (both morally and as a business idea) is apparent, but I am repulsed.
If you want to start a business, find a way to give people value rather than exploiting their desperation and/or poverty.
Having said that, I definitely would not pay the fee. $100 is negligible of a hold and most rentals don't last for more than a week or two in my case (depending on where I am traveling). It wouldn't make sense to pay a fee when the hold is fully refundable and doesn't make a dent in my card usage.