Very good point. For every tectonic plates theory or heliocentric system or H. pylori causing ulcers there are thousands of claims that are plain wrong. Statistically speaking, knowledgeable critics acting in good faith (eg, not having strong conflict of interests) are correct with the overwhelming probability.
You get this all the time with perpetual motion machines. The near certainty of the claim being false leads to confident dismissals that go 'blah, blah, laws of physics, blah blah thermodynamics, therefore can't happen'
The real question to be asking about a claim of a perpetual motion machine is 'Where does the new energy come into being?'.
Citing laws of physics won't help you because any claim to have made a perpetual motion machine is implicitly claiming to be a proof by counterexample that one of those laws is wrong.
Citing the laws of physics in this case is the shorthand way to point the overwhelming number of proofs by example that the laws are correct.
If your law is all liquids flow off a ducks back. Water off a ducks back does not prove it. Acid off a ducks back disproves it. https://i.imgflip.com/7waajp.png
I don't think it is a matter of a shorthand. I think it is because humans have a tendency to express a strong opinion when they intend to express that a weaker opinion is strongly held. Citing laws of physics does not say "Your perpetual motion machine won't work" but rather "I am confident that your perpetual motion machine will be shown to not work".
A single device, made in some garage, that appears to disprove it is simply not rigorous enough to prove anything and isn’t worth third party investigation until the creator has shown they’ve ruled out possible explanations.