I think I've had a bit of experience with training, but in NO way would I ever offer to train anyone's dog, as I simply don't know enough to do that and if you don't know what you're doing, you can make things worse or actually create a problem.
Someone called "CanadianK9Info" posted awhile ago about how to become a trainer and I think the advice is very good.
(My bold letters, as I think that sentence particularly important!)
"The best way to become a qualified trainer is to get a dog and train it, go to dog shows and title it in obedience, tracking, agility etc. Title your dogs all the way (not just beginner level titles I mean advanced). I really feel that if you don't compete in obedience you have no business running classes.
Title your dogs then ask a qualified trainer (another competitor) if you can audit their classes to learn more, work with shelter dogs to gain experience. Join professional organizations such as the Association of Pet Dog Trainers , go to seminars by trainers like Terri Arnold , Connie Cleveland..... it takes years to become qualified, please do not put the public at risk by giving out unqualified advice.
I forgot to mention earlier. You should also be reading a ton of books. Pick up books by authors like Terri Arnold (you can get her books on her website they are called Steppin Up to Sucess), Ian Dunbar, Karen Pryor (Don't Shoot the Dog), Jean Donaldson (she is a trainer in Montreal... has written some great books including The Culture Clash etc.), Joni Andersen (The Latchkey Dog). Read everything you can get your hands on."