I've pasted CMP's description of their service grade rifles below. Generally, the SG rifles will not have pitting on the metal or split/cracked wood, but will have a few dings and parts from various makers. The description is the very least you can expect, while most will be very nice rifles that rate well above the description. I think issue M1's were required to stay within 4 inches @ 100yds and were known to be extremely reliable.
If you can make the trip to one of the stores and pick them out, you'll be able to get a couple of really nice rifles.
SERVICE GRADE: (Good to Very Good)
Service Grade Rifles show less wear and better appearance than Field or Rack Grades. Good to very good condition. Rifle wear will be exhibited by worn and mixed colors of the parkerized finish. There may be some minor pitting on the metal parts. Wood will be either Walnut, Birch, Beech or other variety and will be basically sound but may have minor hairline cracks, dings, scratches and gouges. Wood may not match in color or type of wood. Wood may be of new production on Service Grade Garands. Bores will be generally good with only minor imperfections. The barrel crown may be nicked, but the muzzle will gauge less than 3 and the throat erosion will gauge less than 5.