What the jeweler may mean is that under 1 carat the GIA does not issue certificates, it issues GIA documents, an abbreviated kind of paper. But he is being disingenuous since he is not offering you that either.
You have to be the one to decide whether or not you want to spend $90K without knowing exactly what you are getting. that's what GIA certs (or AGS, they're just as good) do for you. The in-house gemologist may be good but he/she does have some pressure on them to bump up the stones color and/or clarity just a little. They are not impartial like the independent gem labs. And with diamonds, they may look very pretty and also sometimes even the same to the naked eye, but there is a real price difference between a .95 carat and a one carat for instance, or between an F VVS and a G SI1.
to me, a good reason to forego a certificate i(EGL USA can also be okay, I wouldn't bother with IGI or some of the others) is if the diamond is really, really cheap, which is not the case here. You also are not going to have as good resale value (such as it is) without a certificate unless you have some name on the bracelet, such as Tiffany. So if I were you, in this case, I would go elsewhere.