@Dave42 -
I have been hosting about a week and still haven't figured out my strategy here. I have chosen to have a flat rate for up to four people for the moment, but here are the factors that influenced my decision:
-I provided one private room with a queen bed and private bath. My accomodations for persons 3 & 4 are a couch.
-While a 3rd/4th person do use an extra towel and washcloth, it doesn't cause me to run an extra load of laundry, and I can't imagine they use much extra utilities overall. Water is cheap in my state, so the potential two extra showers doesn't seem like much.
-The biggest potential cost would be the extra breakfast, but my guests so far haven't taken much for breakfast. A man took two apples. The party of two ladies yesterday used a little coffee (which we make every morning anyway), a bag of tea, and one packet of instant oatmeal. I might consider having a charge for extra guests if that changes drastically with more guests.
-When considering a surcharge, i thought that $3-4 per extra guest might be fair. Airbnb requires a minimum of $5 charge per extra guest. As a parent to three kids, I know I would find being charged $10-$15 over the advertised rate annoying because hotels typically do not do that. Hotels typically have strict limits on the total # of guests per room, and any extra charges are for services (possibly for extra towels, or a roll away cot, etc etc).