If you take offense easily, please, don't read on. If you want to see my likely slightly-insultingly accurate comments on the majority of the previous complaints, you must be nuts. -_-
THOSE are the reasons why you dislike the GTS? What the heck are you trying to get, MEW? Some other Legendary?
I've not really tried the Negotiation, but that's because I don't really care what I get, since I help distribute those Event-only and hard-to-get Pokemon. But, seriously, if they keep showing they don't like what you're offering, then change it! You shouldn't use the Negotiation if you don't have anything worth offering that you won't give.
If you can't get exactly what you want, just use the Deposit option. Deposit say, an extra Mewtwo (for example) from your LG/FR/SS/HG games, being legit and all (just reset them and go get another. or exploit the Emerald Clone glitch, whatever floats your boat), then set what you wanna get. No loss to you and you get what you want in about the same time it'd take you to find that one trade that happened to be asking for something you DO have to trade.
I dunno if the clone trick from D/P works, but whatever. The game's not going anywhere. Oh, and that too: IT'S A GAME, remember?
Nintendo should monitor EVERY SINGLE POKEMON that goes onto the system... HOW THE HECK DO YOU EXPECT THEM TO MONITOR THAT KIND OF NUMBER OF POKEMON, genius?! Statements like THAT are prime evidence of Bill Cosby's definition of Brain Damage. Seriously, do you even TRY to comprehend just how many Pokemon are constantly going in and out of that system? It's an impossible task, and they've done what they can to at least try to have an automated check-system. It doesn't always work because they're just raw data it's easy to make a fake that something automated can't catch. If you think it'd be so easy to do, why don't you go and apply to spend your life doing nothing but verifying legality of Pokemon on a trade server at 800 Pokemon a minute. Bah.
It's not Nintendo's fault, and not even their problem that some gamers are just idiots and either cheat some things to broken/fail-ness or freak out at the stupidest things. If you got an 'obviously faker than fake' Pokemon in a trade then just breed it like you were gonna do ANYWAY! (If you seriously think someone's just gonna offer the cream of their crop and you're gonna be the lucky one to pick it, go get your head examined.) If it's a Legendary, then what the heck are you wasting time focusing on them for? Cripes, get something worthwhile. If you need those Legendaries sooo bad, then go get the game(s) they come from and obtain them yourself. If they're event-only ones you want, find a trade-thread and contact someone who will trade you one.
Of course, considering that you have the Pokedex data means that you've already been ABLE to get it in the first place (with a very few exceptions), you are just weird, since the only thing you'll likely get out of the trade is that extra percentage of odds for a Shiny-hatch Egg.
As to Shiny Legends being all over... I dunno. I only think a very few Legends look good Shiny (Mew, Rayquaza, Cresselia, Giratina, Keldeo, Meloetta are about it for me). I mean, seriously, I am sure I will laugh in the face of anyone that faces me with a Purple Kyogre, even if they wipe me out with it. (that would COOL though! >_< )
Cripes, do I waste space/'breath'. Oh well. Let's see who's gonna yell this time. sigh.