Just bought a black car only a few weeks ago myself.
Hopefully the scratches you have are just surface and the best product that ive used is called Scratch Out. Can be purchased from most motor factors and basically when rubbed into the mark, breaks down the paint around the area filling in the scratch. Quite good but as said, only for surface marks.
Halfords do a kit, primer, paint and laquer which isnt bad for deep marks, hadve used it myself and wasnt really happy with result. Metallic paint cannot really be fixed 100% unless you go to a spraypainter andd get the exact colour madeup. Im a picky fecker so that would be the only option for me.
If it helps, I always try and park away from all sorts of heaps that you might see in a carpark. I know its literally impossible to guess if your car will be scratched or dented depending on the cars surrounding spaces but from experience, the ones drving the dirtboxes, dont really care about anyone elses property. Only happened to me last night by a f/national in a opel cadett. Opened her door against mine and then looked to see if anyone was looking. I said "Excuse me, but you just slammed your door against me car", "Sorry she replied. I said, "Yeah, sorry isnt gonna pay for repairs".
Then she drove off. Little dent and little sratch. P|ssed me right off.
But what can you expect from idiots like that.