Before we get into setups, services and construction I want to talk about some very common issues and misconceptions about Ukuleles and buying.
These are things every Uke player should know.

1st. This is a BIGGIE !  "I went into a store, and when I played the instrument the frets were sharp and hurt my fingers or hand. It must have been a badly made or cheap Uke".
While it might be a cheap or badly made Uke the reality is ...............
Virtually all Ukuleles are made in very humid areas. So even if the wood is "seasoned" (dryish) there, it still has a fair amount of moisture in it.
So, facts and physics, wood is hygroscopic, it absorbs and releases moisture. Think of your kitchen sponge it shrinks up when not used and puffs back up when it gets wet.
The finger board or fret board does the same thing, but when it shrinks the metal frets don't. So they stick out called "fret sprout".
Back to cheap / badly made, this is easy to fix and most companies file them down before they leave the factory.
So when a Uke gets to New Mexico and our extremely dry climate the wood shrinks up and leaves the ends of the frets sticking out, "fret sprout".
If the shop / dealer doesn't take the time to file them back it will be painful and annoying to play. This is the dealers responsibility to maintain, and is critical to the instruments playability.
I've had more than a few customers come in who have had bad experiences with a brand and assume it was the companies or manufacturers fault. Not saying that sometimes it is, there are some really poorly built Ukes out there. But it should have been addressed before if was given to a customer and for sure before they take it home.
FWIW....... this process can take some time, I've had to file down the ends 2-3 times after the initial set up. There will be a point usually in the winter where it will have shrunk down as much as it will and if the frets are filed then it shouldn't be a problem again.

2nd. Frets are uneven and or are flattened out, some of the notes buzz or don't play well.

When the fret board is built is should be completely straight, flat and level. If it's not when the frets are installed they have no chance of being level. After the frets are installed they should be checked for "level", that they are flat and level from the nut to the end.
Too many companies just take a file or sanding block and slide it back and forth until any high spots in the frets are removed.
Frets are rounded and the top "crowned" so the notes play more cleanly "true" and it is more comfortable to play.
In the extreme they can be completely flattened and in some cases barely there.
In normal cases the frets should be rounded back over (re-crowned or dressed).
If this is the case on a Uke you are looking at or playing run away ............
You shouldn't buy a Uke that has this issue and then have to take it someplace to get it fixed, assuming it can be.
You can learn more about this in "Setup" and why I feel that "Every Uke deserves a great setup".
No matter the price, if you don't enjoy playing the Uke, you won't play it and that is the cost of a poorly made and set up Uke.

OK, so I guess I have to talk about this, intonation, or the lack of it.
So for those that don't know what this is, intonation has to do with a Ukulele being in tune across all frets the on the fingerboard from the 1st fret at the nut to the 12th fret, not just the open strings.
If the open note on the string sounds exactly the same as the fretted  note on the 12th fret (although an octave higher) then that string is in tune and intonated correctly.
If the notes do not sound the same, with one of them sounding flatter or sharper than the other, that string has an intonation issue.
Ukulele's are like Classical guitars in that the saddle, the bone or similar material in the bridge is normally a straight piece of material.
It is a trade off or compromise where it's close but some strings are more "correct" intonated than others.
This can be more pronounced on brighter, clearer and louder instruments. Some people can hear this, others can't. It can be checked with a good digital tuner.
Compensated saddles. This is when the break point, where the string crosses the saddle is moved forward or backwards to change the intonation.
Electric instruments usually have adjustable saddles to easily dial in the correct intonation. Ukulele's don't, and unless a precut compensated saddle is available for your Uke it will have to be cut by hand. While this isn't rocket science it is a slow exact process.
FWIW: most people and manufacturers in the industry live with this, some makers are slowly adding compensated saddles but most are not.
NOTE: I am working on sourcing blank and pre cut saddles in order to offer this as a service.