After buying the air 2 it's time to go out with the old. It has a small dent in the frame, but works great, what's the fair price on this? Thinking of listing on Craigslist.
eBay's median price is around $220-230 (16 GB wifi model third generation iPad). BestBuy has a trade-in offer where you can get $150 and then an additional amount depending on what you're buying: $25 for an iPad mini 3, or $50 for an iPad Air 2.
I haven't been monitoring prices on Craigslist, but hopefully those numbers are helpful to you.
You should generally expect to lose 40% of value compounded every year. Assuming that you bought your 32GB Cellular iPad 3 for $679, and given that it was launched 2.5 years ago, the price is roughly 679 * .6 * .6 * .8 = ~$196 at the most. Add the dent, and $150-$170 is actually quite reasonable.
I just traded in my iPad 3 to Best Buy today. Their guarantee is that you'll get at least $150 + a $50 coupon toward an iPad Air 2. For my 16 GB iPad 3 (wifi only) they gave me $167 + $50 coupon. That is probably more than I would have gotten from eBay. I'm pleased.
I traded mine in at Best Buy - a 32GB white Verizon Gen 3. I got a $185 gift card + a $50 coupon for a total of $235 back. I felt that was a great deal.