Originally Posted by
Hydrated
It's hard to say EXACTLY what the problem is without laying hands on the wheels, but when breaking spokes the problem is nearly always low tension... followed by uneven tension. Due to the quality of modern spokes (even cheap ones) it is hard to break a spoke by over tensioning it... you'll prolly pull the eyes out of the rim first.
Also, if the "dork disc" is removed and the RD limits weren't adjusted properly a chain that went over the top can mangle the spoke elbows on the drive side. A quick visual inspection can check this out. It's become part of my inspection when buying a used bike.