Sorry to hear that. It always sucks when you get a bad deal. But I
certainly wouldn't chuck the pump without dismantling it. When I got my
Edwards pump it was seized, though turning the pulley by hand freed it.
On dismantling I found only a minimal trace of dirt and corrosion - not
enough to affect the performance of the pump once it had been cleaned
out, but enough to seize it because of the very tight clearances. These
pumps are never easy to turn over, even when it perfect condition, but
naturally the motor should be able to turn it! I would dismantle it and
see what you find. A clean might solve the problem and be all that is
required for a de-soldering system, but you're likely to need to
replace the seals, gaskets and oil if you want good performance. Also,
you'll get to see the mechanism, which is really cool. It was so cool I
took some photos of the mechanism and turned it into a GIF animation,
which I meant to put on a web page about my vacuum pump project. I
never got round to it, but one day I will...

Good luck!

Chris