Hard to tell from the pictures on the exact condition, but it looks decent...several things are not original or missing. We sold our '78 which was in GREAT original condition (5,000 miles) for $1100. So $300 is good for a runner. Those bikes get 80MPG.
I think you got a good buy at $300, with a title. I'm just responding the way I am because I'm glad we sold ours as it's a learner bike, or a farm bike and no more than that.
What makes them not so good is the 6v system. Even makes them harder to see in traffic. You need a specific charger that will do 6v. Fun bikes at first, but very gutless with a top speed of 58 MPH (according to the speedo) on a good day. I don't like turning them in curves because there's literally no weight and not much support. Cleaning the oil filter sucks though and requires some removal and several new gaskets.
The pipe isn't original, and they had a really cool pipe. It's missing some side covers. I think the front fender is on upside down. Looks like the tank has it's share of dings.
I've always heard a rumor that CB125s will brick easily if the oil is not changed on a regular basis. That should be your very first step.
