I've been dealing with this attitude since I started working at home 7+ years ago. Everyone in my family thinks I'm free to: run their errands, drop them off/pick them up from the airport, wait at their house for the cable guy, take someone to the doctor's office, etc.
Thankfully I moved 70+ miles away so it's a little better, by my brother and SIL mentioned the other day that since babysitting cost $5 an hour, it sure would be nice if I babysat for them as a Christmas gift. Considering it would cost me $15+ in gas, plus 3 hours to get there and back, PLUS whatever time I have to actually babysit, it's a LOT less expensive for me to write them a damn check for $30-50 to pay for a babysitter!
