A motivated student will usually make a long-term commitment to learning guitar, so it makes sense to 'shop and compare' before choosing an instructor.  For twenty years, I have offered every potential student a free consultation.  There is no better way to compare instructors then to actually sit down and see in person what each instructor has to offer.  I know if someone truly wants to learn guitar, they are going to be motivated after the free consultation.  That is why the free consultation works for me, while at the same time it provides the student the best opportunity to shop and compare.