Of course, there is no guarantee people will still be taken in. That, in fact, is the major vulnerability of glamour spells. Many people refuse to be affected. Their will effectively negates yours. Others will know something is wrong and will think you untrustworthy.
Generalized glamour is far better than specific glamours.
A good glamour is subtle and doesn't tell someone something. This limits the problems I've listed. One type of glamour that I've used successfully is for when I'm walking home late. It suggests I'm confidant, aware of my environment and am not a good target for crime. The way I do this is that I visualize how I want to appear.