During winterizer season, all of the random "sprinkler guys" come out of the woods to make a quick buck off of you. Most of them have never installed a sprinkler system and don't have the knowledge of the plumbing and the requirements to properly winterize the system.
There is more to a winterizer then just blowing out lines, and in fact, the "blow-out" portion of the sprinklers is actually the least important part of the winterizer. The real work comes in properly draining the part of the system that can't be blown out. Not handling that part properly is where the issues occur and the costs add up.
We encourage our customers to use us, the professionals, to handle the maintenance of the system so it can last for years. We understand that saving $10 may seem attractive, but when it comes down to it, is it worth the headache you may have if it is done wrong.