This promo got me to bite though it took a while to find a game worth trading in. I went with Saints Row The Third: Full Package for $23.
Here's the full fine print and I bolded a few important bits:
Terms and Conditions
To receive the Promotion:
• Initiate a video game trade-in between June 13, 2013 and June 30, 2013.
• If the trade-in is accepted, you will receive a confirmation email.
• Add a qualifying item described in the offer to your Shopping Cart.
• The discount will be applied automatically to your purchase of the qualifying item.
Terms and Conditions:
• The promotion is limited to one per customer. If there is more than one eligible item in your Shopping Cart, the promotion applies to only the lowest priced item.
• The discount is valid until August 31, 2013. Amazon reserves the right to cancel it at any time.
• If your video game trade-in is not submitted in accordance with the instructions, or is not accepted, you are not eligible for the promotion and you will not receive a promotion.
• If you do not purchase the qualifying item when the promotion is in effect, the discount will not apply.
• The promotion applies only to qualifying items sold and shipped by Amazon.com. It does not apply to items sold by other merchants on the Amazon.com web site.
• If you return the qualifying item purchased to obtain the promotional code, we will subtract the value of promotional code from your return credit.
• Does not apply to orders placed with 1-Click. The offer may not be combined with other offers.
• Shipping and handling charges apply to all products.
• Offer good while supplies last.
• Void if copied, transferred, or prohibited.
Unless any of the games listed on the link page release before 8/31, I don't see how the $10 would work towards anything that's not a pre-order.