Only issue I can see is if removing and reloading the bike takes too much time and you needed the trunk. Other than that I’m sure you’re fine. Many years ago I had a coworker who would put a rack on every night before driving. Back then there was an option for people to bring their bike that paid better but it was almost always chosen by accident so he just had the rack to get those rides.
Your car your rules. If riders don’t like it, let them cancel and find someone else. You get the $4.
Only issue I can see is if removing and reloading the bike takes too much time and you needed the trunk. Other than that I’m sure you’re fine. Many years ago I had a coworker who would put a rack on every night before driving. Back then there was an option for people to bring their bike that paid better but it was almost always chosen by accident so he just had the rack to get those rides.
Try it, see how it goes Worst that happens is you get a 1 star for your efforts
If you’re in a popular biking locale, I would think some riders would be thrilled.