Most cars have had some repair work at some point in their life. People get dings, someone accidentally scratches the paint, etc. etc.
Not long after I got my car I got 2 dents on the bonnet from somewhere (I'm guessing kids playing). But screw it, I could spend £30 getting them removed or spend £30 on fuel. Fuel is more fun!
If you're genuinely worried about your car. Get the RAC or AA to do a thorough inspection of it. They won't pick up BMW-specific stuff. But they can tell you exactly which panels have been resprayed, or if there's repaired accident damage. They'll be able to give your car as close to a physical as a car can reasonably get. Then you needn't worry about it anymore (you'll have a certificate!) and can get on with enjoying it.
Of course if you're still worried after that, maybe sell up and get a brand new supermini with a long manufacturer's warranty. Worrying isn't good for you!