I own a rug cleaner and always put Bissel in it. Put the wrong stuff in and you might get the type of result folks see when they try soap instead of windshield wiper fluid.
This is just not a big expense issue for me. Maybe it would be if I cleaned my carpets more often.
Very helpful...not
Let me clarify my comment. Detergents represent a large class of compounds with different properties. You need to match the properties to the application.
This is a surface chemistry problem.
Carpet cleaning is a low water application so you need a detergent that works well in low water and does not leave an unwarranted residue.
Using the wrong type of detergent can create problems, such as the windshield wiper issue. You don't want to put together a mix that is difficult to get out.
You don't want to have to use excessive amounts of water.
Using another analogy, would you formulate your own motor oil? Motor oil and detergents share the fact that they are engineered for a purpose.
Here is a decent basic discussion of detergents.
https://en.wikipedia.org/wiki/Detergent