You really can't tell well by looking as honest shot out wear is done by powder attacking the throat. On a benchrest rifle, you might lop .25" from both ends, rechamber and recrown to a great varmint gun. not worth it IMO.
IMO, there are 3 ways to check a barrel you are worried about:
1) run a tight jag and patch down it. Ideally, you would clean it first. Any serious damage you can feel, or see at the crown. Typically bores in modern guns with modern ammo, are hard to damage, IMO. I also look hard at the overall wear and handling marks. It is hard for me to imagine someone treating the exterior with care and then ramming a steel rod up and down the bore to the point of damage...
2) you could shoot it. If you can shoot it or see a test target you trust, you can get a good idea about what you are buying. I would bring quality 22-250 ammo in a 45-50gr weight with a flat base bullet.
3) a barrel maker or barrel fitting gunsmith often has a borescope. They will scope a barrel for a relatively small fee. It allows them to see quite a bit, but I'm not sure it could be related well to group size. You can see throat damage I believe.
If you guess wrong, a new barrel can be put on from a couple of hundred to a match barrel at about $600.