Exactly. Hydro stores and the like are able to mark up prices out the ass simply because you can't find the products anywhere else and most people are more than likely very wary of ordering their grow supplies on line and having them shipped to their grow house.
It's essentially basic economics. OK, maybe not basic. One has two choices: he can either study and save money by purchasing products that weren't "officially" approved for Canna cultivation, or he can make the choice not to study and have someone else choose his inputs, hereby saving the time and the necessary effort. It all depends on what it's worth to the individual. With all this in mind, I assert that hydro stores are not ripping off their costumers, as they provide a service quantifiable in monetary terms.
Simon