Check the crown of the barrel if it looks uneven then someone was careless with cleaning. If the price is right as far as dirt cheap then buy it. A decent gunsmith can fix it for not too awful much. You would just have to wait till he gets to it.
A bore light helps to see inside the barrel. It is a hook shaped clear plastic light. Cost is less than $20 last time I looked at one. Look for pitting in the bore, and see if the rifling looks uneven. Most used rifles in .308 are in decent shape. Many get lost to the pawn shop when someone needed bill, gas, or grocery money. They had every intention of getting it out, and something else happened that prevented it. I have seen it happen more than a few times.
There are a few flea bitten dogs sometimes. Someone that was carless with one decided to offload it for what they could get for it to be rid of it. Sometimes there is a great one that just needs a little TLC, and turns out to be a fine shooter. A good friend bought a rifle from a distant relative that had an old rifle that would not shoot worth a darn. He sold it to my friend for a song. Turned out it was not screwed into the bedding properly, the scope mounts were loose, and the barrel was dirty, and copper fouled. Two hours of work, and was tack driving accurate. He has taken many white tailed deer with it since.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.