I'm a big fan or thorough rinsing after the use of any carpet shampoo. A rinse agent will work better than plain water and should be available at your local carpet cleaning supply store.
Not to :argue with anybody who doesn't use an extractor, but my Century/Ninja sure works a lot better than my Bissell and Hoover units, and those work a *LOT* better than my wet/dry vacs. It seems to be a matter of how powerfully the extractor can spray hot liquid; the sucking up the liquid part isn't the issue (though a small-orifice nozzle is a *LOT* better than a wider one). FWIW, I run a Bissell "upholstery nozzle" on *all* such machines. Just the right size orifice.
Other than the spraying/heating of the liquid, the Bissell/Hoover units basically just *are* wet vacs, although some of mine also have brush attachments that compare with running carpet brushes on a polisher.
Anybody thinking of doing nasty interiors should check out how David Fermani does it....and IIRC he doesn't use an extractor, which makes his work even more impressive in my book.