Full disclosure (and actually I'd forgotten about this until now): I admit going into a theatre ONCE when I hadn't seen the show but was walking by and really had to use the bathroom, but the show was getting toward the end of letting out, I knew where the bathroom was, and I knew one of the ushers — I told him he could watch me go straight into the bathroom and come straight out (which I did). I wasn't doing it as any kind of pattern.
Also, if you really want a playbill without having seen the show? Just wait in front (not AT the stage door), and see who discards them. You can usually find clean ones sitting on top of planters, recycle bins, window ledges, a table of the nearest Starbucks...
"This thread reads like a series of White House memos." — Mister Matt