Those wear marks are called Sig "smiles". You will find them on all Sig handguns. Sigs are some of the most accurate handguns made. The smiles come from tighter tolerances than most handguns, including Glocks. They are purely cosmetic and should not deter you from buying a used P250. As to the scratches inside the barrel, they are not normal. I have never seen anything like you describe. It's most likely something the "user" has done. If you can, put some rounds thru it and see how well it shoots before you buy it.