We have been using Responsible Pest Control since September. They are always super professional and come during their scheduled appointment window. For once a month service, they are very reasonably priced. If at any time during the month you have a problem, they will come back out and re-spray. Granted we are just heading into scorpion season, but I'm hopeful that we won't have a problem! We found our first one outside last month, and it looked like it was dying (tail out, sitting on a rock for a good 45 minutes), but they still came out to re-spray for us. Based on their website, they guarantee if you DO find a scorpion in/around your house, it will be dead or dying.
Nothing but a positive experience with this company.