Earlier quoted context omitted.
It obviously depends on the field. But if the YouTube video explains clearly why X technique is sub par, and demonstrates the failure mode I'd believe it over a tradesperson. Say you see your mechanic tighten the nuts on your wheel hub in a circular pattern instead of a star pattern. Would you point this out?
I'm not sure about your particular example but it seems to me like this argument could be made for something like software engineering too, ie someone watches YouTube on the top web frameworks or SWE best practices and asks you why you're not doing it the way they saw. Sure, the video might show failure modes too, but that doesn't necessarily mean that it's always the right way to do it, there are tradeoffs everywher…
The contractor just needs their work to fail not-before the warranty period expires.
Think of them more like foreign software contractors being paid per JIRA ticket, rather than in-house long-career developers.