I'm thinking about picking up a Pink WM-55 I've found, listed as not working. The seller says that he put batteries in and can definitely hear the motor, but the player doesn't spin. 
Is it safe to assume that this is a belt issue? If so, is there anywhere I can find out what size belt the WM-55 takes? 
I'm new to this sort of thing, so I'd like to know what I'm dealing with at least a little bit before I pick this up. 

If the seller's observation is right, it's most likely either a torque issue or a belt issue. Keep in mind though that these walkmans are not the easier ones to disassemble.

What would I need to do in the case of a torque issue? 

Chances are it's just a belt change, this can be tricky but I'm pretty sure it's easy on the 55.  Seller is a member here by the way and seems to have a decent reputation.

Oh, well, neat then! Perhaps I'll give it a buy. 

Does anyone know what size belt the 55 takes?