Hey Mark
Well, despite the subtext in your postings I take the chance of "picking a fight with the admin guy"
You don't seem to have much confidence in the Thai/Bangkok tour agencies, which I think isn't quite fair. From my daily experience I'm every day seeing lots of limousines, van cars and buses with tourists from various tour agencies, and the tourists are seemingly pretty happy with the services provided to them - so don't be too hard on them.
On the other hand, on my frequent trips to Bangkok I have also - among mostly nice ones - experienced pretty annoying taxi drivers, who definately knows about tourist venues "not opened today, because...", or "you should meet my uncle, who owns a jewelry shop..." or "this is not my direction", or "no, I won't switch on the meter, price is fixed...", etc.
What I try to say is that there are good guys and less good guys everywhere, you just have to be sensible in your choises.