I'm seeing this increasingly on adverts.
That once a piano is moved i.e. put on the back of a pickup or a van of somekind and drive. It will need to be retuned.
Secondly just how sensitive/tolerant are acoustic pianos to temperature variations?
A place I am going to move to in a couple of months. In winter it goes down to -13C while in the summer it can get to +35C
Even in one day I may turn the heating on for a few hours to get it to about 15C, but will turn it off when I leave the house letting it cool to 4-6C because heating is expensive.
Potentially next year is even more whack. As its 34C 100% humidity day and night. When I get in I'd turn the air conditioning on reducing this 34C 100% humidity to 21C and 30% humidity, this would utterly kill an acoustic piano right?
OK. First of all, the piano never knows where it is. There is nothing intrinsic to a change of location that makes the piano go out of tune. The main principle to remember is that it is mainly a change in relative humidity that causes most of going out of tune. This may happen from . . .
1) Moving from one location to another that has a different relative humidity
2) Staying in the same place and having the relative humidity change. As I explain to my customers here in the upper midwest, "Just sitting here your piano experiences the equivalent of a ride between Arizona and Houston every year."
Other factors that are minor are . . .
1) temperature -- in and of itself, not as a factor in changing relative humidity. Normally change in temperature (like hot to cold to hot) will not cause a permanent change in tuning once the piano restabilizes to normal temperature.
2) Vibration and jostling. Can happen and sometimes on certain vertical pianos, the whole plate can be flexed just by moving or having the casters at a different level. Sometimes it might jar out a poorly set string. Or, if it is a grand piano moved on its side and the dampers are off the strings, there can even be string breakage caused by perpetual string vibration on a cross-country move.
3) Playing. Heavy playing can contribute to strings "letting go" if the piano is not well stabilized by frequent tunings.
One other consideration . . .
What do you mean (or accept) by "out of tune"? What is (or is not) acceptable for a piano being used for recording sessions may be perfectly acceptable for a casual player. The one might need at least touch up between sessions on the same day. The other may be OK for 6 months.