Hey Ginou,
I liked your post because I like the fact you are attempting to make make life better for yourself. Well Done!
As to your question, we have a variety of location owners from diverse backgrounds. Every one of them want to make $. Make your pitch, honest, sincere and polite. We offer 40 to 50%, dependent upon the quality of the location. I often say that we'll start at 40%, and if at the end of 3 months, the location generates your minimum (we like to hit at least $50 per month our end) then we'll increase the split.
Let them know you will call ahead when you come to empty the chair and you will ask them to count it with you. They like control and this shows you're transparent and likely honest.
Stress that you take all the responsibility for repairs and the location's responsibility is to keep the chair clean and call you when anything happens (breaks/acceptors jammed, etc.) as soon as possible. When the chair is not working, no one makes $.
For Example,
Hello, this is a really nice facility, would you happen to be the owner?
Have a sheet with a picture of the machine you want to place. Describe the type of massage it gives and how much people like it or how you like it.
A laundry was our first location. It was self serve. We found that as long as the location was supervised the chair did ok. Unsupervised sucked bad. Chairs were damaged, unplugged and vandalized. We only go for supervised areas now.
Anywhere people wait will work. Children's play centers are good because the parent can sit and watch.
Anyways, good luck. Do your research and choose a chair that fits your requirements. Some can be quite heavy and not so easy to manover through doorways.
Also remember that you will be fixing these things when they break, so hopefully you've got some mechanical abilities or access to someone who can help.
Good Luck, and if you need any more information or advice, feel free.
Retired Guy