If both pairs are DS, then the person receiving the Concord lows are losing a little bit of money in the trade. It's not like either of you are getting ripped off badly. But because you mentioned that the other person's Gammas have been worn, I think you should get a lot of close ups of the shoes to determine the conditions of the shoes. Also, you may want to post some pictures on here so we can also determine the condition of the shoes because it's likely that your 9/10 condition of a shoe differs from other people's definition of 9/10 condition. Depending on how much the Gammas have been worn and what shape they're in would be the deciding factor for me in this trade. But if you go through with the trade, and you're happy with what you've got, then that's all that really matters in my opinion.