In a Monster House, since I almost always carry a Petrify Orb, I immediately use that. Else I just go with the flow and hope I succeed.
OK, something annoying, though, is when, in PMD2: EoT, I was going on a mission to arrest a bad Pokemon. Long story short, as soon as I entered that floor, I not only encountered the bad Pokemon (and I do believe when you encounter something like that, you can't use Orbs), but I landed in a Monster House >.>
I still used the Petrify Orb after defeating the bad guy, thankfully. My partner's Hydro Pump really came in handy that time.