It completely depends on the quality of the repair. My father owns a body shop and i've worked in it the last 11 years. If we repair a total loss it is just as good if not better then it was from the factory. So there are shops out there that do quality work but they are few and far between. Most are butchers. with that said.. here are a few things to look for.
Seams- see if the door was paneled... if it was walk away. Check the seams in the trunk jam and door jam to see if a quarter was put on... If a quarter was put on and you can see where it was put on.. walk away.
Core support - Look for factory spot wells on either side of core support.
Blisters / Lines - Look for blisters or lines in the paint or seams, If it were welded and the welds werent sand blasted they WILL come back. now or later.
Gaps - Look at headlight gaps, door gaps, fender gaps, hood gaps, windshield/rear glass/door glass gabs (especially if it got a roof.)
Interior- Look for busted interior pieces.. or loose interior pieces. to put on a roof that all has to come out..
Roof- Ask if it were welded or glued on. Dont be afraid of glue, some are stronger then weld.
Paint- Look for runs, dry spots, dirt hunks, orange peel, blends, color match... If it was a quality job you shouldnt be able to tell. dont be distracted by "its shiny"
Rear end/ suspension - Roll overs sometime bend rear ends... and bend other suspension parts. Make sure tire wear is even and it drives straight as an arrow with no vibrations. Look underneath, if you see metal with paint chipped off it was bent or stressed there... run away.
Make sure you get picture of it before it was fixed. Legally they have to disclose those. See what shop fixed it and research them. Also see how long ago it was fixed.. and any problems since then.
So.. if it is a perfect and quality repair i'd say 70% of book value. if it is nothing less then perfect leave it there... If you can see something wrong with it.. that's only 10% of what's wrong that you cant see. and dont get distracted by the aftermarket goods on it (tires/wheels, lights, ect)... look past those to see the real car.