Im not sure if I should post this somewhere else or not so I just made a new post.
I know this has been a problem for a while, so I thought so hard I had a brain overload and exploded and grew a new one which had an idea (just joking). Anyways, I think that we should only be able to trade when we are lvl 20 or the max lvl or just before it. Then, it is 100% that they will be in that episode. Maybe, you can't trade items that you have never got before. And if you want it, the other person can just show you. I hope this has solved all the trading problems!
From a person with an exploded brain (just kidding)
- Dr. meh