I have not yet had the luxury of buying a uke that was set up properly (my plastic fretboard Flea being the exception). Either that, or they dried out and created sharp frets before I got them. None were advertised as set up, so I knew it was a crap shoot when I bought them, and one was a gift. On all of them I watched some of the excellent videos on YouTube about fixing sharp frets on guitars, got myself a nail file with a smooth edge, some masking tape and sandpaper, some super glue, a small hard rubber hammer, and went to work fixing them. It takes time, but its not rocket science.
I have found 3 distinct problems that I have had to fix:
1. Some frets jut out beyond the width of the fretboard (probably due to drying out of the wood). Those need to be filed down at roughly a 45 degree angle to meet the fretboard again. If you don't tape the fretboard first, you will most likely mar it up.
2. Most frets on cheap (under $200) ukuleles have never been properly rounded after the fret wire was cut off. They have very sharp corners. To fix them, you need a file with a smooth side on the narrow edge. You can then lay that side on the tape next to the fret and proceed to round the fret. There is a good YT vid on this
HERE.
3. Some frets are just up too high on the edge because they were not properly set, or they popped up. Many can be pused back down and a small drop of super glue will hold them. A real luthier would probably remove them and reseat them. Some I have just put a drop of super glue on the edge to fill the gap. Then, I sanded it down with very fine sandpaper.
I understand that sometimes a minor sharp fret problem can be fixed just by re-humidifying the neck, but I have not run across one that easy yet.
If I ever buy a new expensive ukulele and it has fret problems, I am gonna be pissed.