Stargate is easy to sell at $2,000+. Secret Service is tough to sell even at $1000. I would never do the trade because Secret Service is not a great game and will get boring quickly, but if you did, I would want at least $1250...and honestly probably more. If you don't want Stargate anymore, I would sell it outright and then go after a game, you'll be better off financially in the long run.