@Erin197 - Use the links I provided. They will send you to the Co-host Marketplace where you can write what you'd be willing to do as co-host. When the homeowners add you officially as their co-host, all the conversation and negotiation can be found in the back and forth on the Airbnb platform. Thus your "contract". Should anything go awry with the hosts, there were be a recond on the platform of what you agreed to do for them for the price negotiated. This would give you back up should you need to make a claim via the Resolution Center. Guess what I'm saying is, if you have to go after them for any payment, I personally would prefer to have Airbnb work with me through the Resolution Center and Co-host Marketplace than have to hire an outside attorney.
That being said, it looks like you are talking about the guest houst listing on your profile. Based on the work they are asking you to do, the market research, the upkeep of the listing profile, contacting the guests, being available 24/7 to the guests for questions and issues, well, that seems like you are doing the bulk of the work. The work (actually the "labor") is the communication, set up and the "selling" online - getting the bookings, bringing in the money. Typical labor costs for many businesses run between 25 and 35%. It actually kills me that Airbnb suggested only 20%.
What you are willing to work for as a percentage of the overnight cost should be based on the number of hours you work per week to make that money, if that makes sense. So for instance,
if you spend, let's say 10 hours doing everything you need to do (including cleaning) to settle a 2-night stay, at 15% + cleaning fee, you make $8.50/hour more or less. If you take 20% + cleaning - wage goes up to $9.75. However, if the reseration is for 5 nights - and maybe you have to spend 3 more hours answering questions, "being available", the extra cleaning for a longer stay, at 15% your wage goes up to $10.70/hr. Now I don't know what kind of reservations you get at this location or how much time it takes you to book that reservation, but calculating out what you will earn for each type would help you decide if 15%, 20%, or 25% works for you. Personally, I always look at the shortest reservation since that will always be the least I will be paid, but you may prefer to average it out.
BTW, the average hourly salary for a Customer Service Representative in the US is $13.47 according to Payscale. A cashier makes $9.15. It seems to me that you're doing more work than a cashier and a living wage is calculated to be $15/hour.
Hope this helps.