What makes it hard today is that many homes have loans higher than current market value. Another issue is that many builder's credit rating has suffered due to being over extended when the market slowed/stopped for new construction.
Many builder's margins are very thin these days so taking a home in trade ties up their working capital. If they have a difficult home to sell, and yours is less expensive and more marketable, they might trade to lower their carrying costs.
I would be willing to discuss your specific situation if you like.