This article is from the Piano Purchase and Maintenance FAQ, by Isako Hoshino firstname.lastname@example.org with numerous contributions by others.
One of the supposed disadvantages of aural tuning is really
one of the advantages -- that no tuners do the job alike, and
that the tuning may vary from time to time. One could as
easily insist that an advantage to player piano is that they
mechanically reproduce a given performance over and over.
Further, the ear remains the best judge of intonation.
A tuner who tunes without the aid of an electronic tuning
device occasionally will be decidedly disadvantaged due to
sinus congestion resulting from allergies and/or viruses.
Pianists generally like a good tuner's "touch of personality"
in a tuning. Aural tunings, because they require individual
judgments, vary from one tuner to the next. Any given tuner
may, at one time or another, be preferred over another
because of their particular "flavor" of tuning. Because
pianists have different tastes, it is sometimes necessary to
shop around before settling on a tuner whose tuning pleases
the pianist. The level of skill among technicians varies, as
well, and this, too, contributes to whether their particular
method or "flavor" of tuning is desirable.