When people people hire a piano technician to service their piano, they expect that the technician will leave the piano in tune. This is a perfectly reasonable expectation. However, there are situations where it is impossible for the technician to leave your piano perfectly in tune.
Due to the nature and composition of pianos and their strings, they possess a characteristic known as inharmonicity. When a tone is produced, there are several harmonics sounding within that tone. In pianos, the harmonics of each tone or string are actually slightly sharper than what they should be mathematically. Generally, longer or taller pianos have less inharmonicity than short pianos. A piano technician makes adjustments to account for each piano's inharmonicity to leave it in tune.
Very short console pianos and spinets (shown in the photo above) have the most inharmonicity. So much so that they cannot actually be in tune with themselves. This is most noted in the bass section of a piano. The bass will never sound correct on a short piano because it is not correct and cannot be. The inharmonicity is so high that the harmonics of a single tone can never match up properly with other notes within the piano. This is one reason why short pianos, especially spinets, are not good pianos for young people, or really any people at all. They can destroy one's sense of pitch. When a technician tunes a very short piano they must make a lot of compromises in order to make the piano sound in tune. Even then, it will not sound very pleasing to most people.
Another significant disadvantage to spinets (the shortest of pianos) is in the placement of the action within the piano. Spinets are characterized by the fact that their action is positioned lower in the piano, behind the keys. A spinet can be classified on the exterior as having a music rack that is taller than the back of the piano. Because the action sits so low within the piano, it is very difficult to complete even the simplest of repairs. There are also extra parts linking the keys to the action that make it so the piano is not as responsive as others. Another reason not to ever own one. The existence of extra parts creates another problem. Those extra parts are prone to breakage resulting in higher cost of ownership.
The best advice I can give is to buy the tallest or longest piano you can afford. If that ends up being a spinet, so be it. If you can avoid a spinet I highly recommend it. If you already own a spinet or similar short piano, that's okay. Just realize that it does have some limitations.