Best advice I can give you is don't trade them, sell them. Most dealers give about 50-60% of market value on a trade. The nicer, rarer, and more desirable a gun is, the bigger hit you'll take. Unless it is something you have absolutly no use for, no desire for, or simply do not care what you'll get for it, sell it outright.
That's not a "knock" on dealers. It's just the nature of the business.
Edited to add: Now that I've read your other post it changes things a bit. If you're going to offer to trade heads up with someone, you simply offer this is what I got, whatchagimmie? The legalities will have to be handled through an FFL if in different states. If you're in the same state, at least here in Virginia, I'd say "Meet me at Shoney's Sat morning. We'll talk."
