Hi
This is an interesting one. There's no policy. It's a feature you either offer, or don't. Disclaimer I have an EV. I fully expect that I will find a way to plug in my vehicle at the house. It's a different mindset. There is no direct comparison to hosts paying for my gas. This is a transformative technology, not an equivalent one.
People who buy EV's in early adopter tend to be more environmentally focused and/or purely done the numbers and realised its cheaper to run then combustion engine cars. And it's going to grow whether you personally agree or not. You could say NO to charging EV's as a house rule but you eliminate a section of the market.
So as a host, you want to offer as much as you can without increasing your cost base.
So to the point of the other replies, what is the issue? Is your electricity bill going up? If so, do you have time of day different rates, perhaps you could politely ask if your guest could charge in off peak? It's like running a washer, dryer or other items. I would have thought as a host and looking at your cost base, you would be ensuring you are watching your energy consumption regardless, especially given the Texas electricity market is quite unlike others in the US.
Given the guest is an EV owner, they do have some idea of charging costs so they will likely be quite amenable to adjusting their charging times. It's too late to say no by the way. And they are probably charging once a week or so? Is it daily? Depends upon the distance they are travelling.
I once tried to charge for Caravans (RV's you call them) being plugged in to my property, and had a small daily rate. But the arrival of EV's have changed all that.
I have installed an EV charger which means I can tick the EV box that I provide a charger so people can search on it. It's provided for free. If you don't have that box ticked, it doesn't mean they can't charge their vehicle at the property though. They'll find a way, like your guests have. I kindly ask the guests if using the charger to charge in off peak if possible.
I haven't had huge usage of my EV charger btw, but it's a feature to atrract bookings. Given its not a fast/super charger, just an 'everyday' charger but just a bit better than plugging straight into a powerpoint on a trickle charge, guests probably won't be wanting to pay for it anyways. As an EV owner, I will happily pay for fast or super charging, but not for trickle/slow charging.
So the upshot is, you probably can't charge for any EV charging in a domestic usage, even if you install a EV charger, but you can appeal to the guest to charge at a time that's cheaper assuming you have setup your electricity metering like this.
Hope this helps
Kind rgs
MK