I couldn't agree more. First the best place to get the best price on a new or used vacuum is always at an independent vacuum dealer, because they have to fix all the stuff the department stores sell so they get price breaks from the companies on the same items.
If you have ever been to a big box store and asked an associate anything about a specialty product they won't know. Bagless vacuum cleaners cost a lot more to operate than a bagged model and trap the dust better (please look up bagless vacuums and allergies to see what I mean). Suction doesn't mean as much as people would think. If you were to suck on a straw and put your finger on the end of the straw it does not matter how hard you suck. You're going to pass out from not breathing. You need airflow (a good volume of air) to get carpets clean and yes, there are several that are cheap that will work but only for a short period of time that is why they are cheap.
Your thoughts are good, just your facts are confused. As an independent vac dealer for over 20 years I have the facts and can give the proper advice on these items.