@Sebastian1017
I only host long term guests now, but when I hosted short term ones, this was also sometimes a problem for me. I do have a washer/dryer and didn't mind guests using it (in moderation) if they were going to be here for several days, but I found that some guests who were travelling around would turn up with loads of dirty laundry expecting to do it all for free at my house. Personally, I think that's just rude. I'm renting a room, not operating a free launderette.
Others would put the machine on every day just to wash a t-shirt and pair of socks.
So, I started charging £3 a load, which is extremely reasonable by London standards, especially as this was a service wash. I mean, I didn't trust the guests to not break the machine or to not put it on a ridiculously long hot wash, so I would wash, dry and fold their clothes for them, all for only £3, including detergent and softener. Yet, it's amazing how many people took exception to paying £3 and reacted like I was trying to rip them off (even though it was mentioned on the listing). I'm not just talking about people on a really tight budget. Some of these people were coming home with piles of shopping bags from Harrods!
And yes, I had guests who were hand washing whole loads of laundry in the sink and hanging it dripping wet in their rooms or sometimes all over shared bathrooms despite this being prohibited in my house rules. I have three clothes racks they could use, but they would still do this. I remember one pair of girls who were repeatedly told to stop and said they would, but I could see from the window that they were still hanging their wet clothes on the curtain rail, on top of my silk curtains!
Now that I host long term guests, they get free use of the machine. I just ask them to buy their own detergent. Because some people are really excessive, I added to my rules that they can do one wash per week, but really, no guests pay attention to this at all! I explain to every guest which cycles are appropriate for small loads (they almost always wash really small amounts at a time) and some guests are conscientious and follow these instructions, but many don't. There are some guests who just don't care about water or energy usage and will put have the machine going for three hours for less than half a load.
With energy bills soaring and also my water bill rising due to this kind of excessive use, I'm tempted to start charging for use of the machine again, but I don't think that will be very popular with long term guests.