I do agree that the GTS is flawed in that respect. It's filled with people you expect something for literally nothing. But, I think I've got it figured out so I can get what I want. And it's not all bad - if you look, you can find decent trades. It's mostly the 'in-demand' Pokemon like starters or the such that usually have the crazy deals.
Patience is key, being quick at shifting through the offers also helps (hate that you have to switch out and in...).
Then, find some Pokemon that are in demand, and breed them, for instance starters. Use these to trade for things you want, and as long as the trade isn't too unreasonable, you'll get what you want, as your deal would be fantastic compared to the others. Check what people want generally besides the legends or level 100 Magikarps to see what people want - does change from time to time.
Work your way up - breed the stuff you get for 'higher' things. Attach items like berries that you have multiples of that are rare. It works for me - I usually end up with what I want sooner or later. There's always the one-off 'easy' trade where someone offers something good for a easy-to-get thing - or a 'demand Pokemon' - that needs some luck however.
Or, just use the Wi-Fi and FC's - that works too and is definately simpler. :)