I think Rabby is having the same problem, the history is the thing that people are scared about. Not knowing about this TM with its low hours but used look is off putting, Rabby's on the other hand has been passed around like an orphan so buyers are put off from it.
With a porti it is cheap to fix and most of us have had portis to fix anyway, a TM 2nd hand is usually for an upgrade from a porti so the buyer is infact in the dark.
Personally if you are at the stage where you are looking to get a TM to cope with extra work I would get a new one, put £2k down and pay the rest over 4 years or something, after having 2nd hand TM's I feel the new TM route (unless you are a mechanical whiz) is the way to peaceful sleep and profitable days.
Shaun