Set the rules IN CEMENT up front. For example, will you be willing to watch the child if he is sick? What are the rules about pick up and drop off time? Some parents take real advantage of this. If the parents are so many minutes late picking up, then it is so many dollars more per quarter hour, or whatever. I once knew of a daycare that charged $1/per minute after 15 minutes past regular scheduled pick up time. I felt bad for the Mom one day who locked her keys in her car and couldn't get to the daycare on time.... she was frantic!
I ONCE very briefly considered taking care of another baby. They were casual friends in the area and had a daughter just a month before I had my first child. I knew she was going back to work and was looking for child care. But I bit my tongue and decided to keep it just DD and me for a while. I figured if I decided to wanted to offer later, I could. Anyhow, I made the offer to watch her daughter one day on a holiday when her daycare was closed. Since we were friends I offered for free. Well, she showed up with her DD that morning, hands her over, and runs out the door explaining that the rash is "probably just roseaola and her fever is gone!" and out the door she goes!! I had the girls separated the entire day (far apart in the same room, each in their own exersaucer) and washed my hands CONSTANTLY. That made me really mad and rather soured our blossoming friendship. I felt that she really took advantage of me by handing over a sick child with no advanced warning. And it was especially frustrating since she KNEW I had my own child there who would be exposed to this!
Anyhow, like I said, make the rules up front!.............P