I have to agree that for guitar, a teacher LIVE if possible is a must.
The guitar has such minute, subtle technique. Everything is important: the angle of the hands to the strings, fingering, the left hand's moves on the fretboard, how you hold the guitar, the angle of your wrist. The sound is affected by every one of these aspects. Someone looking at you can correct you. And you'll build muscle memory to have good technique. I was so surprised to find that the guitar is as difficult an instrument as cello or violin. It's almost a secret--our guitar "salon" was joking with me that no one outside guitar players will appreciate that it's so difficult. It's worth learning, it's not unsurmountable, but a teacher is a must.
Ukes: Mainland mahogany tenor, Eleuke Tenor Solid Cutaway Sunburst
Guitars: Yamaha GS-90, Marcario flamenco negra, Cordoba Protege 3/4