Yes it is difficult to cut hair, thats why we train and practice for a long time! There is no magic course(or wand) that will turn someone who has never done hair into a good all round hair extensionist.
Most of these companies give you training that is geared to an experienced hairdresser. For somebody that doesnt know how to handle or section hair correctly, most of it would be too fast, and too in depth for somebody with no prior knowledge or experience.
The reputable companies recognise this and only train hairdressers. Unfortunately lots of companies have sprung up offering to train people as hair ext in the full knowledge that it cannot be done. They take your money, and print you a cert, and you will have no real idea what you are doing. You risk being ripped off big time.
I do expert witnessing in court cases involving hair ext disputes, most are "dabblers" who insist they are "qualified" because someone showed them for 2 days and printed off a cert on a computer. In reality you do not satisfy the assumption that you are "properly trained and qualified" when it comes to disputes.