ok... i'm not too well up on selling, but generally if i'm buying second-hand, i try to get it for around the 50% mark- if you sell it at that, it'd probably move pretty quickly. if you're willing to hold out a bit longer, you could maybe get around 70-80%, which, if you're not desperate to move it immediately, it's probably worth holding out for.
as always, depends if there's someone who just wants it, you can never predict things perfectly. considering the credit crunch, it might not be the best time to sell either...