The problem with a used converter is you don't know what you're getting. A converter is a sealed unit, and you have no way of knowing what's right or wrong with it unless it's cut open. Sure you can visually check the hub (nicely polished with 800 grit), the fresh paint job (from a rattle can), drain some of the oil out of it (nice and red, just put it in), but is the one way roller clutch just about ready to go away, how about the bearing(s) that may be inside it are they any good, are the vanes on the turbine and pump coming loose?
If it's a high stall, how do you know it's the right stall for your particular combination? I've seen enough used converters, both stock and high stall apart, to say that buying a used converter is a total waste of money.
To quote someone else on one of these threads "a used converter makes a great door stop".
You may get lucky on buying a used converter, but you're buying blind.
