@Summer62
I had one of those types my first year of hosting so I can totally relate!!!!!! Even with rules, it's hard to physically BLOCK someone from doing laundry when they have access and they are intent on doing laundry regardless of rules.
My overuser was a 4 month long-term (exchange student) guest in my single occupancy guestroom. I actually did ask (very nicely) that he stick to our 1 load per week quota several times. He was all nice and smiling, apologizing saying it won't happen again but he ran out of socks (or underwear) and just continued to to a load every 2~3 days, alternating between whites and colors. We have a 16kg top load washer and he'd throw in 7~8 items (counting each sock separately) and set it to "full load". I think the largest load of laundry I saw him do had about 12 items right after coming back from a 4 day trip and he did 2 loads - whites then colors.
Believe me Henry and I were very tempted to do something like what @Paul154 suggests and we actually DID do something similar....... just not with the washer - thought it would be too obvious 🙂
In addition to including a laundry rule limiting # of loads if you have a way to limit or block guest access to the washer/dryer or lock it up, do it. If they have to ask you for access when doing a load and you have rules, it's easier to say no or charge what they would have to pay to go to a laundromat.
Most guests are great....... but there are always a few that WILL take advantage if they can.