Just my two cents and observations:
Newer, well priced locos with TMCC or Legacy are selling. Older locos...post war or MPC or LTI....without the modern electronics....are NOT moving.
Postwar in Like New or better is still decent. Postwar in lesser grades is almost dead.
Most MPC is slow moving or near dead. However, it's very cheap....and is a good source for budget minded or $$$ limited people. Stuff that we drooled over in the 1970s and 1980s has really bottomed out. And when you buy that low, you can't really lose money on it. While some of these have outdated electronics and no scale fidelity, they run like tanks and are almost indestructible.
Ross and Gargraves track and switches move fairly well....as are most "layout building items".
With the exception of some limited quantity Atlas items, rolling stock is really slow to move. Post war rolling stock in less than Very Good condition and almost all MPC rolling stock in any condition....even Like New or Mint...is not moving at all and some times, can not be given away.
So, in conclusion, it all depends....like always.