[Alex W]

I'd be weary of any used wheel pilot. The parts for them are getting slim and wheel pilots are devices that don't live the easiest life. Since the units usually include 3 or 4 major components (computer, fluxgate compass, control interface, and wheel motor) you have to trust that the old unit was properly removed and includes all parts to be useful.

For instance you'll probably come across the Raymarine/Autohelm ST4000, which is easy to find use. However almost no parts are available for it anymore, which is why they are easy to find used.

The Raymarine X5 (last generation) and Evo (this generation) wheel pilots work very well.

 

[Alex W]

because of that you can get a couple of them(st3000, 4000) for cheap and use till they bust

Except that the failures are generally in the same place over and over again. If one has all of it's parts in good condition it will sell quickly to someone who wants the parts (like the clutch lever which breaks easily).