I am trying to buy a geared DC motor from a large, international auction site. However, most listings do not list the amp draw. The vast majority explain the motor like "12V 30rpm 25mm DC Gear Motor Micro DC Gear Box Motor" or the like. My motor controller lists as the maximum power it can handle is 12v by 2 amps. Is it possible to determine if the motor controller can successfully handle a motor if I only have access to the voltage, rpm and size?
If you refer to this motor on the listing you have a table with the rated current.
For the motor you specify, assuming it is this motor, it should be 0.16 A so your controller should work.
It's not possible to determine the current only by the RPM, voltage and the size of the motor.