On the Yahoo! App, you should have a pop up when someone offers you a trade.
I have offered people a trade who only use the mobile app and not online, they never check their pending transactions because they rarely have any. I have texted them and they say they never saw it. I suggest when you offer someone a trade, it pops up when they open the app, only the first time after a trade is offered. It could say something like "Team Baseball has offered you a trade, click to view"