If the sandblasting is done well, there should be NO flecks of rust left in any pits. Assuming that's the case and there are no rust flecks left, I'd recommend priming with two coats of epoxy primer the same day you get them back to prevent any flash rust from appearing. A "bright metal" sandblast leaves the metal in a very raw state and flash rusting can begin right away. Even by touching, moisture from fingerprints can begin the process. If you cannot prime right away, I'd recommend applying some Picklex-20 to protect the metal until such time that you can.
If there ARE rust flecks left, the sandblaster didn't do the job properly and I'd demand the situation be corrected at no additional cost.