I teach guitar up to around grade three and love it!
Very important!! Lots of young guitarists need helps in this respect, especially when starting out. Guitars need tuning every time they're played.
A cheap tuner will be very useful: Tiger sells one for about £6. Free apps are handy. The books I've recommended on this page come with tuning tracks on their CDs, which is actually a better way of tuning than by using a tuner since the guitarist learns to listen and tune up based on what they hear rather than see on a display. The same goes for the following video:-
Buying a guitar
I tend to buy both second-hand and new guitars in person, usually at Harmony Music in Dorchester and the music instrument heaven that is Absolute Music in Wallisdown.
I recommend the following books for learning to play guitar:
I am liking Trinity Rock and Pop exams and ocassionally use Rockschool.