Arsenal refinished means they were completely are partially re built depending on condition in a Russian state arsenal. They used new, or good condition used parts for the refurbs. The majority of SKS's are arsenal refinished, their is the odd one that is unissued, unrefurb but they are pretty uncommon. Most have new barrels and are in good shape.
SKS's are fun, $500 gets you a rifle and 1120 round of ammunition. They are not target rifles by far, but are good plinkers and are a conversation piece.
Their is a forum where the SKS experts hang out. Its the "Red Rifle" forum. Their are some stickies at the top of the forum that are just about the SKS and are very informative. have a look their and all your questions will have an answer.