I found this information which I find interesting in a book, I will summarize it very briefly

Never try a guitar where there is no deathly silence.
There is no point in performing your own repertoire

Instrument test
It is an objective test that serves to establish the quality of the instrument and to highlight any imperfections.

Verification protocol
– Tune your guitar very carefully
– Compare the correspondence between the harmonics and the real notes at the 12th fret on all the strings.
If the 1st string (e) and the second string (B) have a gap in the two playing modes at the 12th fret, the
problem lies in the strings and not in the fretboard. The high strings often have imperfections, Segovia when
he changed the I string (e) tried a dozen of them, and when he found the right string he held it as long as
possible.
Check the correspondence of the harmonic on the 19th fret of the 1st string (e) and the 2nd string (B) perfect
strings are a minority if you come across a perfect e string keep it as long as possible. If on all strings at
12 fret the harmonic deviates from the real note the guitar fretboard is imperfect or the bridge is at the
wrong distance.
– Test all the strings at each fret with medium intensity checking the decay of each note, the test must be done
both with all the strings open and by stopping the 5 unplayed strings, the enrichment of the sound by
resonance but also the single note isolated will be evaluated. The notes will have a greater or lesser sound
decay, it will be necessary to verify the absence of “note lupo” (Italian expression traslatable into wolf
notes, I don’t know how are called in english) that decay immediately after the pluck. If you find wolf notes
on the 1st or 2nd string discard the guitar.
– Verifying some notes by playing them in different positions of the keyboard evaluating their intensity and
timbre response, this requires a certain skill of the evaluator. Evaluate how readily the guitar responds to
the vibrato obtained by moving the finger along the string without bending.
The notes from the 8th to the 12th fret on the 5th string in some guitars for unknown reasons presents the
fundamental note falls rapidly to make way for the 2nd harmonic of a higher octave, when this is very
accentuated the guitar is to be discarded.
– The 6th string played open in some guitars shows a harmonic of 3 (G#) so intense as to generate a bichord,
this can generate serious harmonic problems as we will have a guitar that plays in E major when I make an E
minor chord with the 6th empty string. To evaluate if the problem is serious, one must play the 6th string
open with a strong intensity and immediately after play the harmonic of the 3rd string very slowly at the 12th
fret. Attentive listening will allow one to evaluate the conflict between the two harmonics (G 3 string) and
(G# 6 string) if the G 3 string is well defined the guitar will be acceptable otherwise we will have a guitar
in hand that will play inexorably in E major.