I'm sure I've read before of a procedure for bus/taxi drivers to arrange alternative transport if they are registered as having a dog allergy? (Which seems sensible... a driver having an allergic reaction is t he last thing a disabled person needs)
I regularly see a guide dog put with its owner while I'm doing grocery shopping... they ate obviously well trained.
I think the unfortunate truth is though that it may be time for an official ID for assistance dogs.. but there will need to be a procedure for registering them first and confirming their training.