I have a local gun store who has about 20 870P's just in...

they all vary a lot in condition....   i plan on at some point sending it into wilson to have they're magic done...

but what should i be looking for between these shotguns to pick out the best?  how do i look for wear and abuse?   should i look down the bore with a flash light... should i just check for simple cracks and wear marks?  ETC

is there anything that you'd recomend checking before i buy one of these SOB's!   Thanks!

The 870 is about bullet proof mechanically, so the main things to look for are excessively worn finishes, pitted or scored bores, and signs of abuse or alteration.

Generally, Police guns are carried around a lot, but seldom actually shot.
I'd pick one with the least external finish wear, or battering of the stock.
Try to pick one with no rust or pitting inside or outside.

You'll need to pretty well ignore crud, fouling, and plain old filth.  Many Police shotguns never get cleaned from the time they leave the factory, so they can be really dirty.  
This can be deceptive.  It can cover up a really good condition gun, or it cover up rust and pitting.

Look down the bore for any rust, pitting, dents, or bends in the barrel.  If they will allow it, remove the barrel so you can look down both ends and check the chamber.
Usually what looks like streaks down the bore is actually leading.  What you're looking for is rust or pits.
The bore may not be grade-able until you can clean it out.
Check the chamber for rust or pitting.  It's not uncommon for shotguns used with modern plastic ammo to have rusted or pitted chambers.

Check the barrel for a "squashed" muzzle, dents, or bends.

Open the action and look inside for rust.

Check the the bolt face for rust or pits.

Check the stock where it joins the receiver for cracks.

Check the fore end for cracks or splits.

Open the action and watch the shell lifter to see if it moves smoothly up and down as the action is operated.

Stick you finger inside the receiver and check the tension on the shell stops.

Give the magazine follower a push up the tube with your finger to check tension.

The action should be smooth with no catches or overly gritty feel.  Keep in mind that it likely hasn't been cleaned since it left the factory, and may be full of grit.  Take this into account.

Close the action and pull the trigger.  It should have a reasonably smooth, slightly heavy pull.

Open the action, pull the trigger and HOLD it back.  Close the action, release the trigger.  It should reset smoothly.  Pull the trigger again, the hammer should drop.

Cock the gun, put the safety On.  Pull the trigger, the hammer shouldn't drop.  Put the safety Off, pull the trigger, the hammer should drop.

If it looks pretty good, it usually is.

When you get it home, disassemble it, including the magazine tube, remove the bolt and carrier, and the trigger group from the receiver.

Give it a good cleaning, check over for any obvious damage, and re-lube.

great thanks a lot faris!