I ran a small time vending business for about 2 years...I only had 5 double headed machines....the best place I had landed was a trucking company with about 80+ employees....I would make anywhere from $60-$150 every couple of weeks.
I did have an experience with a vending machine location service..they'll place your machine for you, but they find really terrible locations.....if I had to get back into it..I would try craigslist to find locations with business owners. It's not a bad deal...buy ur candy from sams club or costco and never fill up the machine all the way is the best tip I can give you, make it look like people are actually using it...ya know?
I had read one guy that had put an upside down Styrofoam cup and some googly eyes on his machine and his profit jumped by 50% although I never tried it...I would, I still got the machines.....the truck plant I had them in went down....and the other locations weren't worth it....in the long run though, it can make you some pretty good coin for not really doing much....and you can write off your candy and gas mileage off at the end of the year.