I just used common sense and reading comprehension I suppose, but I could be wrong. It's not not typical practice for any gun shop to order a gun they don't have in stock, especially under their GSSF program, especially when it's for a newer customer. Then there the fact that the OP went through with the sale, when most able-minded people who could simply walk away because no money changed hands would have done so.
It only makes sense that he paid upfront for the gun shop to special order a Glock (the gun plus shipping) they didn't see fit to have in stock under the OP's GSSF credentials. If the OP hadn't paid beforehand, didn't have to work about a restock fee and refund, and could have simply turned and walked away instead of arguing, I assume (hope) he's also intelligent enough to have done so.