Like you, I've been doing this part time. I've got a full time job and doing this on nights and weekends (mostly weekends). I've got 4 weekly customers and 3 bi-weekly customers. This is just strictly residential business. I haven't been advertising too much but I'm able to bring home roughly an extra $500/month. Like I said I stopped advertising (mainly on craigslist) but I still get calls. If I decided to advertise more, I'm sure I could bring more home but at that point time/daylight becomes my enemy (not enough of both!!).
I guess what I'm trying to say is that you can control how much you make. Sometimes you have to work a little harder for it, other times, not as hard.