I've had the same problem, and was going to start my own thread if there wasn't one!
For the most part, trade has occurred as it has in CiV, with the addition of favors. When an AI wants to renew a deal, the standard "I liked this, let's do it again" pops up, and you can refuse or accept.
The problem is that sometimes the AI pops up and says "Hey, I need some help! How about giving me some stuff for a bunch of favors?" And when you hit "accept," they say "This deal isn't good enough!" Which is very annoying.
On another note, I think the favor to resource ratio needs some rebalancing. Sometimes the AI will offer 1 favor for 15 energy or 3 of a strategic resource, and that seems fine. But a few times they've offered 1 favor in exchange for anywhere from 35 to 80 science. This is ridiculous (sometimes its half the science I'm making), particularly since the AI is EXTREMELY hesitant to trade their own science. Either lower the amount of science they ask for, or have them offer more favors.