Leadfingers is right about problems in the old days, but things are better now. Intonation problems on 'ukuleles are usually down to playing technique issues (the strings are very bendy and require a very different touch from steel ones) and/or poor setup.

A few instruments have construction faults that affect intonation, but very few from recognised mainstream makers.

The most common problem is high action at the nut causing sharp intonation on notes played on low frets. If intonation becomes less sharp as one goes up the fretboard then that is a VERY strong indicator that the nut slots just need a bit of a file to get the action right.

I have set up dozens of 'ukuleles for many people and the only one that actually had a fault that screwed up the intonation incurably was one that I had bought myself: a Stagg concert with a misaligned bridge. All the others intonated acceptably after a setup - even cheap Makala Dolphins.

A good setup and a light fretting technique are usually all it takes!