John Tye Piano Tuner
Signs of a need of regulation include:

Hammers at uneven blow distances
Uneven key heights
Notes that will not repeat well,
Notes that repeat when you do not want them to,
Notes that sound quiet,
Notes that continue to sound after you have released them,
Notes that give a muffled sound but do not ring,
Notes that do not always work
and, for the expert player, unevenness of touch.
If the piano sounds harsh, it will probably be possible to tone (voice) the hammers by needling the felt. I tone a sample hammer to see if you like the more mellow effect. The problem is that it is not reversible without replacing the hammer. With an upright the only way to do it properly is to take the action away for a whole day so that I can take the hammers out and work on them in a vice. With a grand this is not necessary, so I would do the work on site.

regulation, excluding toning and repairs £120
toning all the hammers of an upright £110
toning a grand £60

These prices assume that the job is part of a tuning, otherwise add 25.