Why not think about smarter solutions ?

for example:

Why not define that a rent can only have one decimal place ?
Why not just take a fee for price change (not for listing a card) and add a cooldown-time from f.e. 1 hour for a card who was listed at the rental market and delisted before they can be listed again ?

Why you need this fees - I mean you take already 5% fee from every rental.

Let's say in this way: When you sell your house the estate agent will take a fee AFTER he sold your hours isn't it ?
Would you be glad if he take an additional fee every 30 days just for listen your house ?