I also have noticed that when you need something it is rarely available, but if you start making it then it shows up, still is rare, but once you no longer need it and have it in inventory the Trade HQ is flooded with it.
Lets face it, the advantage is with EA here, they have the metrics written so they come out ahead, its no difference than throwing your money away in Las Vegas, to quote Robert Dinero "Look around, do you think we build huge hotels by losing at gambling"
The new refresh button and its sold thing is ok, but still I think they should stop the travel to a place to buy it, it wastes time and energy.
I have decided that rather than worrying about it, Ill just search as many peoples stuff as I can in 29 seconds before hitting refresh, that seems to work, although takes a huge time bite. But it is what it is and EA has shown they are only in it for the money. So why complain.