Oh sorry I got two stones confused. This one looks more beautiful but the other one is certified. Yes I would tell that seller that you can offer contingent on him getting GIA cert.
Thanks. At first look, this stone looks very windowed in the default pic.
I also had a bad experience with JupiterGems :/ I purchased a stone from them (which they didn't include a proper description for), and they were hesitant in accepting my return. (YMMV)