If a company or individual posting to craigslist is having trouble with competitors, fake posts, harassment, etc., there are a number of ways to get things done. I'm sure that Craigslist, like every other site, makes people jump over a few hurdles before they can get in touch with a live human.
Calories Burned. On average, a 150-pound person burns 91 calories biking for 20 minutes at a leisurely pace of less than 10 miles per hour, according to the Calorie Control Council's Get Moving Calculator. The caloric burn increases to 136 calories when intensity escalates to a moderate pace, 12 to 13.9 miles per hour.
Comparing the Calorie Burn. In terms of calories, a 30 minute treadmill running session at 6mph for an 155lb adult will burn around 350 calories. The same size adult will burn around 260 calories in 30 minutes on a Spin bike at a steady pace. However, a Spinning class is much more intense so you can expect to burn anywhere from 400-600 calories if you push yourself.