As soon as they open the door and I walk in (as they usually like to hide behind it)...I say "Oh, is the person that was in the ad here?"  

And from that point on, it's all about where is the person in the ad?  If they are not here, then you politely excuse yourself and leave.

I've had a few pissed off trannies give chase over the years, so I usually just am as polite as I can be about it.  Kill em with kindness on the way out.

calmly walk out..

http://itchyscratchy.deviantart.com/art/Lena-Hyena-153388793