My laptop has a plastic chassis whose panels click into place (no screws on the outside). When I bought it (new), there was a gap on one side along the seam joining the top and bottom halves of the chassis (1 inch by 3-4mm gap). That is to say that one of the "hooks" was not clicked into place. Also, the panels didn't quite line up by the USB port whose bottom edge merges with the seam on the same side (so it might have been used for prying it open?).
Is this an indication that it might have been tampered with somewhere along the line? The box was sealed and looked fine.