The second thing is money, of course. Not all people are ready to invest in such courses or they just do not have budget for that. This is reasonable. Although we usually evaluate things according to their price, where the quality means more money, this is not always the case with these online marketing services. The big price is maybe just a paravane for scam or poor product. It would be the best if you can talk with someone who already use some service and ask him about his experience. This is very important because if you rely only on forums and experience of the online community, you will be at danger to be fooled by paid marketers, whose job is to write good about those services.
Because of that, the rule number one is that more money does not guaranty the quality.
The rule number two is that you have to choose the service according to the specificity of your business and established business goals. In that way, you will be sure that you will get only you really need.