
Seasonal changes - contrary to common opinion, it is not temperature change which cause a piano to go out of tune, but changes in atmospheric humidity. An increase in humidity will cause the wood in the soundboard to expand. This exaggerates the crown and stretches the strings, thus altering the pitch. The reverse happens when humidity decreases.
Constant Playing—The piano
is meant to be played. However, constant playing means that vibrations
are travelling regularly from the strings up into the tuning pins. This,
over time, will cause the pins to slip incrementally, and the tuning
drifts lower.
Gradual Downward Drift -Even if the piano is not played, string tension will, bit by bit, unwind the pins by tiny increments. Also the strings will stretch, and the pitch will gradually creep lower.
Loose Tuning Pins—Anything loose unscrews more easily (logical isn’t it!). There are some ‘quick-fix’ solutions for loose tuning pins (such as ‘pin-block dope’ and knocking the pins in further). However, loose tuning pins are a real danger signal. To deal properly with loose pins very likely means repairs which will cost several hundreds of dollars (such as replacing the pin block). If looking to buy, there are some instances when a tuner would tell you not to touch a piano with a ten-foot pole – and loose tuning pins is one of them! Don’t ever knowingly buy a piano with loose tuning pins!
WHAT IS A PITCH-RAISE?
A 'pitch-raise'is as its name suggests: the raising of the pitch of the piano to concert pitch (A440)
If a piano hasn’t been tuned for many years (or decades!), the pitch may have dropped significantly. If so, pulling it back up to pitch will result in a large increase in tension on the piano frame. This will cause the notes tuned first to drop in pitch again, as more notes are tuned. This means that the piano really needs to be tuned twice.
CLEANING
WHY DO PIANOS NEED CLEANING?
When the piano is opened up, the action and the keys are removed. The action, the key-bed and other dusty areas are gently brushed to removed built-up dust and grime. This is then vacuumed up. The whole of the interior is also dusted and vacuumed. The keys and the action are then placed back in the piano and tuning can commence. The whole cleaning process might take 30 minutes. With future tunings, a brief cleaning may be necessary, but not as lengthy as the first one (hence the lower charge for subsequent tunings!).

What might need repairing in a piano?
Any number of actions parts may, at various times, need repairing or replacement. These include such things as:
Worn hammer, Cracked or broken flanges, Broken string, Broken hammer shafts, Chipped keys, Broken keys,
A home piano, played
infrequently, might go through its entire life without a single
regulation (although it is likely that it would receive occasional
regulation on some parts each time it is tuned). By contrast, a concert
grand would very likely have some refined regulation work every time it is tuned, and may even have a thorough regulation two or three times a year.
One factor affecting regulation work these days is the increasing number of super-strong synthetic materials which last much longer (the perspex elbows of a spinet piano action can last up to 500 years!). Complete regulation (apart from the initial setting up) for such pianos would, very likely, become much rarer.
WHEN MIGHT A PIANO NEED AN INSPECTION?
Before Purchase—Like purchasing a car, you want to know that it functions well and is structurally sound.
Before sale—if you are the honest type, and want a clean conscience, an inspection is a good idea!
For Repairs—if you suspect your piano has major problems, you might want to consult a technician. If you have been diligent, and have had your piano tuned regularly, hopefully your technician will have kept you up-to-date with anything your piano might need.
If you are thinking of purchasing a piano, you will want to know if it is any good!
Some tuners may also direct you to certain retailers who have a good reputation; he or she may also may suggest which sorts of piano to look for and which to avoid. They will probably offer this advice free of charge over the phone.
Useful Books:
How To Buy A Good Used Piano Author: Willard Leverett
Victorian Guild: http://www.pianotuners.asn.au/
A useful discussion site is: http://www.pianoworld.com/forum/