Everyone is complaining about the dynamic trade values, but it can also work in your favor.
I got together four of my old games (Warioworld, PacNRoll, Retro Atari Classics, and Yoshi Topsy Turvy) that I would never play again/bought for cheap and could work to get some decent money off of a new release I want.
When I first added them to my cart at about 10PM, they were going to give me a total of $14 for all 4 games, and I wasn't that satisfied with that, so I hesitated. Then I came back around 1AM and updated the cart (because I noticed the value on one of the games change by $.25), and the credit they were giving for all 4 games rose to $17.50, so I went ahead and printed their inventory page with the 4 games and the values that I had agreed to trade the games for.
That was a couple of days ago. Today, the credit they are giving for those 4 games is about $14 again. But what does it matter? They are still giving me $17.50 + the $20 off a new game because that's what the packing slip I printed and included says because it was at that price and time that I agreed to trade my games in.
So, while I can see where waiting may significantly decrease the value they give, once you accept the values, that's what you're locked in for, so what does it matter? It's kind of like playing the market.