Speaking from a suppliers point of view I think competition is good for us - if someone really likes and wants one of the systems you build then they will buy it, competition and choice is healthy for the industry.
As for what iveson says about profit margins I'm sure some of the more expensive systems on the market don't cost a fraction of what the companies sell them for but consider the time put into building a professional system, the time involved in negotiating with the client what system they want re poles, tank size, static or mobile etc etc, then you have the aftercare, not to mention the cost of stocking poles, pumps, varistreams, tanks, hose the list goes on and on. If you want to save money then go diy - I have no problem with anyone building their own (apart from the ones which are death-traps). If you want a professional system, safely mounted into your van with a full years warranty then get in touch with a system builder. I do agree though that some systems you see on the market are a rip off.
However I do know that per hour I make more cleaning windows.