A Tech III can be a good buy. There are some concerns: back in the day of the III, the infinity stop was cut into the rail rather than use an adjustable one.
The cam and lens are cut for a specific body. They are each shimmed to the rfdr. If somebody has taken any of it aprt, whether to figure out how it worked, or 'fix' it... it likely needs re adjustment.
The groundglass is smaller than a IV / 5.
It is not as good for lenses shorter than 90 mm
The front movements are more limited than a IV, but adequate. No front tilt, but it has a backward base tilt.
In general, a III works very well, but you can tell quickly why the IV was designed as it was.
The kicker for me would be the lenses. Depending on what THEY are, it is either a neat antique or a hot camera.
Oh. Marflex is the Linhof repair service. Call them, Speak to Martin to find out what can be fixed. It will be pricey, whatever it is.
Good luck.