The way Buck Howard finds his check at the end of his show is not the way The Amazing Kreskin (on whose career the movie is loosely based) used and still uses. The method was depicted differently probably for dramatic purposes.
The scene with the mass hypnosis, supposedly in Cincinnatti, is clearly in the main lobby of the Dorothy Chandler Pavillion in Los Angeles. The banner with Placedo Domingo's name is even clearly seen hanging outside.