There is very little difference between the Japanese brands in those years. Minor porting, suspension, and bold new graffics were the upgrades. At your level, those changes make ZERO difference.
However, there is something you need to know buying ANY used bike: They are ALL clapped out.
Meaning, no one is selling a perfect bike. One of the reasons peopel buy new bikes every two years is because is is almost as expensive to completely rebuild a bike as it is to buy one new. Bearings need to be replaced, shocks need to be rebuilt and recharged, wheels need to be trued and tightened. Almost all 125's either need or will need in a short time bottom end seals. A 10 plus year old 125 will probably need some cylinder work too - if not now, soon. In addition, 125's are usually ridden by kids who, lets face it, don't usually take good care of their equipment.
I don't mean to flame anyone. You might be the exception who takes good care of your bike and you might find one of those bikes that was well maintained, but you should go in there with your eyes open and when one of these parts fail and you have to drop $300+ dollars to fix it, don't let it leave a bad taste in your mouth.