Yes, even an experienced hypnotist or hypnotherapist could be fooled.
The reason being the phenomena of hypnosis does not necessarily mean you must be in a state of hypnosis. In other words, you can exhibit some hypnosis phenomena by being in a normal conscious state of mind.
The person being hypnotized can deliberately not follow the hypnotist’s instruction but just string along, blocking out what is being instructed and then pretend to act out what is being told.
There is a choice in hypnosis – it is whether you wish to co-operate that determines hypnosis’ effectiveness.