One thing to consider, at least in some states, is the effect on sales tax. In Texas the amount of the trade in is not taxed. The last I knew, it was 6.5% on vehicles although it may have gone up a bit since then. Anyway, if one got $15k in trade that would save $975 in sales tax. Probably not as much as the difference selling it first but $1k for putting ink to paper vs. $2k for dealing with selling it might be worth the difference to some people. YMMV.