@Mark-and-Gabriela0
I think with bikes or items used outwith a property, there is a need as such to treat as a separate business - along the lines of pay a deposit in situ and only then get the bikes unlocked kind of operation. If something subsequently does go wrong, then you have leverage to rectify.
You can put any penalty you wish in the house rules, but without having a method to enforce it, the penalty is useless in practice.
I understand you undoubtedly try to enhance a guest trip with access to bicycles, however you should be clear eyed about the probable consequences if something goes awry.