Those guys do come on the show, and very rarely win.
The winners are most often low-profile professional magicians who make a significant income consulting for the famous ones. Inventing and selling tricks is an important revenue stream for many magicians.
So they come on, do some trick that they invented in secret and worked on for years, and give P&T that same childlike sense of awe and amazement that the rest of us experience almost all the time. It's the best part of the show.
Huh, I never thought about "consulting magician" as a career. Sort of like the professional songwriters who work for music labels, ghostwriting for dozens of bands.
Given that these exist, I wonder how many magicians with a signature trick got it from a consultant instead of inventing it. Are a few people creating all the world's magic acts?
You should watch Jonathan Creek - a murder mystery series about a consulting magician. Pure fiction but rekindled my childhood interest in magic. I'm currently, slowly, teaching myself card magic now. Starting with The Royal Road.
In this case it's difficult to tell. A lot of small time acts hit it big with their one REALLY good trick they develop, or just good enough showmanship that there's reasonable doubt.
I've watched the show a few times and I don't know how carefully detailed the rules of success vs failure are, but on a few instances, Penn and Teller announced they had a fair idea of what tricks were being done but couldn't really place it in an acceptable order or say the how/when.
So even if Teller is the magic encyclopedia, he can be fooled, it seems.
