In general pianos in home should be tuned once or twice a year to stay stable. Usually music venues and musicians have the piano tuned before every performance or recording

After a piano is moved to a new home it is best to wait about a month before getting it tuned. Pianos need time to acclimate to their new environment and tunings are unstable until after waiting a month.

The piano strings sit on a wooden soundboard. Wood moves as it swells and contracts due to humidity and weather changes, which alters the tuning.

When a piano hasn’t been tuned in many years the piano usually drops significantly in pitch away from the standard A 440. There are limits to how far strings can be tightened in a single tuning to correct this so a pitch raise is basically when the piano needs more than one tuning to get it in the proper range.

The value of a piano can help be assessed by a Piano technician on a service call. Usually the worth is determined by the age, brand, location and work it could use done to it. It takes some research as to what local pianos of the same general type are going for and a technician determining its current condition.

You need a piano tuner you can trust has the necessary skills which is usually determined by the years they have worked and their experience. But most importantly you need a piano tuner you have a good rapport with and are blown away by how your piano plays after they leave. You should feel addicted to playing after a tuning.

Highly suggest before taking a free piano to have a piano technician at least look at it. Or at the very least make sure every note functions. Pianos are expensive to move and if you get stuck with one with extreme damage from age or water or being outside it may just be a financial burden to even get rid of.

I have helped train curious people and it is a big commitment of time and money for them. It is a very difficult skill that takes years of practice to tune an entire piano. If you think you might like it as a career go for it. But if you are just trying to save money, you won’t. A realistic goal is to learn how to improve a couple notes that may have slipped between tunings, which I think is doable.