You can spray a diluted bleach solution (I think 5%) on the surfaces you want to disinfect. Let it sit for at least 10 minutes and then rinse it off. Any bleach left on the surfaces will evaporate. I'd make sure the enclosure is completely dry before putting chickens back in it. Bleach/Clorox is very damaging to tissues.
When you get birds from an auction keep them away from your other birds in a separate coop or enclosure. I'd dust them for lice, treat for internal parasites, and watch for signs of respiratory disease. The birds should also not be so close to your other birds so that airborne diseases can spread. I'll admit that I've been pretty laxed about quarantining new birds, but I got all mine from private parties that had small, closed flocks. Getting them from an auction is a huge risk though. Some people say you need to quarantine for a minimum of 4 weeks. Also, so not share any tool, equipment, feed bowls, etc between the two groups. You should also change your clothes and shoes before visiting your existing flock.