I've bought some content for G9 and tried to work with it, but I pretty much only do male characters. G9's breasts have an odd effect that occurs when the are reshaped to look like pec muscles or when flattened out to appear like an undeveloped chest. They look too sharply defined compared to the rest of the musculature in the cleavage and underbreast area, sometimes with a beveled effect. It can be compounded by the texture and normal maps, but the effect can carry through to clothes so it's definitely a shaping issue.  

I don't expect any fixes for it, female characters sell a lot more and I think G9 was made with that in mind.