Been doing a little research, before I go blasting off half cocked and beat the boogers out of somebody with my monitor muscles. Here's what I got...
The RTS auction lists the frame clearly as an 18", with an 18" seat tube and a 22.5" top tube. My understanding of GTs says that's an 18, like my Zaskar. Those measurements listed on the auction match my Zaskar perfectly. An 18" RTS has the measurements that the seller advertised, a 16 does not. A 16, measures up as 16" and 21.5". SO...I hit up the seller to do the right thing and accept my request for a refund.
I got sass instead...I don't know how to measure a bike, I don't know how to measure a GT, He thinks I should enjoy my new tiny bicycle. Have a nice day.
Not so fast, princess...
I sent him a response telling him he's wrong and I expect him to do the right thing when the frame, that leaves my house tomorrow, gets to him. Refund buddy. Do it.
I opened a dispute to start the clock, but I hope it doesn't get that far. The only thing I can figure is that seller either, 1) measured the thing wrong, or 2) 'optimized' his measurements to get the size up to 18, a more common size.
We'll see what happens.