I'm with you Jane. I used to offer my washing machine as an amenity - but a nearby fellow host friend of mine told me the story of how they had someone completely abuse that privlidge with them, and ran the washing machine 24 hours a day, actually going out and bringing back bags of laundry (in other words, he was running a commercial laundry busines) - the guest then tried to call airbnb and claim that he was never able to check in and demanded a full refund. a total scam .
But my local laundrette charges £4/load for a wash and about £2-£3/load for dry (depending on how wet and what type of cloth) - say £7 for a load to wash and dry. Now, if you had about 4 or 5 loads of wash to do, that's £35 - or you could find a £30/night airbnb that lets you use their washing machine, and do as many loads as you can in that one night.
I'm quite lucky, because I don't have a tumble drier, it would be difficult for people to do that. I have a small washing machine, and a drying rack. However, I decided that It could easily come off the list. If I have guests staying for more than 4 or 5 days, I'll offer it to them free of charge for a few loads. Anybody else is directed to the local laundrette, which is only about 80m from my front door.
L.