I think what is not being addressed is the original question...
How do you respond when caught?
I disagree with Richard on one point; professional magicians can and will make mistakes. Being professional does not mean that you always turn in a flawless performance. I do agree that sometimes you can perform flawlessly and still get caught. This often may suggest a flaw in your presentational approach that emphasizes method.
Let's face it, [censored] happens!
What really distinguishes you is how you handle the situation. To some, being a "professional" establishes an expectation that you have the core techniques (both methodical and presentational) down and should be able to perform them 100% of the time flawlessly. Actually, the only thing "professional" really means is that you are paid to deliver what you promise.
In practice, things can go wrong: you can lose the card, drop (or misplace) the load, have mechanical equipment fail, or, in the case of close-up, have a spectator "interact" in an appropriate manner unexpectedly. In the chaotic place that is "real-world" performance settings, one cannot account for every detail, we can only make contingency plans for when something does go wrong (and it will).
All of this can be minimized thorough careful planning, persistent checking and rechecking of equipment (including proper maintenance such as replacing batteries and oiling movable parts).
When we perform magic, we are painting a mental picture that is reinforced by visual occurrences. Audiences are generally only aware of what we want them to be aware. They may have an idea of what you will be doing, but not know the details. There is good reason for the axiom, "Never tell an audience what you are going to do."
The problem is less one of technique and more one of Guilt. If things go wrong, our perception tends to close in on technique. In a white-hot blinding moment we mentally retrace our steps seeking an answer. Regardless of an answer we suddenly realize that we are not alone and we must go on. The stress on this moment is intense and can color our approach from then on in. We make the mistake of turning in when we should turn out.
When things do go awry, don't panic; proceed in an appropriate manner (including addressing your own surprise). Respond to the audience reaction, choose an appropriate action and commit to it. Ultimately you must finish successfully.
If you complete the journey, any mistakes you make will either be perceived as "a bit of business" or may ultimately contribute to the audience's conviction about the overall impossibility of what you do accomplish. (There is a reason why "magician in trouble" is such a compelling plot for laymen.
Keep a confident air in your ability to conclude a piece successfully (and satisfactorily). You may not get to where you were going, but you might arrive at a place that is even more interesting because of the journey.
When designing presentations, I rely on a technique I call "branching" to plan for contingencies. I script out the course of action that I intend to take. I then examine possible opportunities to "branch" off to if the unexpected happens. This could be a mistake, a failure or, on a positive note, a potential interaction with the audience that opens up a new train of thought. The possibilities discovered by studying "branches" also contribute to a more logical, coherent performance. Discarded "branches" are not lost work, but stored responses.
You have prepared for the eventuality. This in turn makes you a more confident performer.
The biggest benefit of being a professional performer is that you have more opportunity for trial and error, which when applied by a thinking performer can make for a more intense, and interesting experience for our audiences.
And isn't that what we want?