Reading verification output correctly
The single most common reason somebody gives up on verification is a warning that has nothing to do with whether the check passed. Reading two lines correctly solves it permanently.
The line that matters
A statement that the signature is good, naming the key it was made with. That is the result. If it appears, the message came from the holder of that key and has not been altered.
The warning that scares people off
A second line saying the key is not certified with a trusted signature, and that there is no indication the signature belongs to the owner. This is not a failure and does not qualify the result above. It is a statement about the web of trust, which is a social layer almost nobody participates in, and it appears for practically every key anybody ever imports.
What the warning is actually saying
That you have not personally vouched for this key, and neither has anybody whose vouching you have configured your machine to accept. It is answering a question you did not ask. The question you asked was whether the signature is valid, and that was answered on the line above.
How to make it stop
Marking the key as trusted locally silences it. Doing so is a statement to your own machine and to nobody else, and it is reasonable once you have compared the fingerprint across independent sources. It changes nothing about the cryptography either way.
A genuinely bad result
A line stating the signature is bad, or that no public key is available to check it against. The first means the content and the signature do not agree. The second means you do not hold the key it was made with, which is a different problem with a different fix.
Why this matters more than it sounds
A verification step that people abandon halfway is worse than no step at all, because it produces the feeling of having checked without the fact of it. Most abandonment happens at this exact warning, on runs that had already succeeded.