all 1988-90 had stickers changed all around to IROCZ (Iroc badge on towards back of door). Prior Years from 1985-1987 had Iroc on doors only ( front part of the doors) but Z28 badges on other parts of the body. 1988-90 also had the square shifting knob instead of the round one like 1985 to 1987.
hope this helps. Also $ 7,000 is too much for a car with all those miles, especially if not original and not a 5.7 engine. I know no convertibles were made with the 5.7.
Also make sure it's got the multi fuel injection and not carburetor.