The OCR is a compact-geometry frame. Measuring the BB to seat height really tells you nothing about the size. That number will vary depending on how much seatpost is showing. The size of the bike is on the frame somewhere, the seller just needs to look for it. If he can provide the size, compare your fit measurements with the geometry on Giant's website for the frame size. Random measurements from the seller aren't very helpful.
Oh, and +1 on it being a good bike. If it fits, and the price is right, you won't be disappointed.