If the motor is built by someone else, they can fall back on the excuse that some piece of their plans was not done to specification. Sending a motor to be verified to a wholly independent source to be thoroughly peer reviewed would allay any fears that it is a scam. Especially since most of these kinds of hucksters - be they trying to sell perpetual motion devices, star charts, or cancer curing water - often refuse to put themselves under the independent investigation of a competent skeptic, because as soon as they do as James Hydrick et al, the free ride is over.

However, I imagine that it doesn't actually matter how many safeguards you placed onto the test, or even how many people verify under stringent and independent conditions that it doesn't work. There will always be another excuse.