Being able to afford the ticket is a privilege, I'd like to know who I'm seeing before I use that privilege.
Back to the topic - I have actually had TKTS employees tell me when a performer is out. These were both unscheduled outages - Megan Hilty in Noises Off*, and Jane Krakowski in She Loves Me.
* this was rather funny.
Me - "Do you have tickets for Noises off?"
TKTS booth operator - "Yes, but just so you know, the star is out from the matinee"
Me - "Andrea Martin? Oh no!"
TKTS booth op - "Oh I meant Megan Hilty, but yes - Martin's out too!"
Caption: Every so often there was a rare moment of perfect balance when I soared above him.