As with all professions, music teachers have a few bright stars floating over a sea of mediocraty. Uke Whisperer's experience is very unfortunate, and the teacher appears unscrupulous for taking his money.
That being said, demographics are such that there are far more excellent guitar instructors than ukulele instructors. (Unless you live on the islands, of course, you lucky bastards.)
Unfortunately, I have yet to meet an ukulele instructor that is worth the money. There are very few guitar instructors that I find suitable either.
The truly exceptional guitar teachers that I have met have all been multi-instrumental, and will appreciate the differences (as well as the similarities) between the various fretted instruments.
That being said (as a multi-instrumentalist, myself) I reject the premise that there is an incorrect way to play the ukulele (or guitar or whatever). The ukulele is a wooden box with strings and frets. Do with it as you choose. Specific techniques can be associated with STYLES of music, but should not constrain your exploration of he instrument, itself.
If you are a beginner, and you cannot find a suitable local instructor, I would recommend the book/Internet route to ukulele enlightenment. Be aware, however, that there is a lot of real crap out there professing to be instructional. Once you reach a higher skill level, you should seek out a MUSIC instructor (regardless of Instrument) who is able to improve your musicianship. That will make you a better player.