I've had a couple of good sales via SEDO. My question to you is, have you had better luck with setting a Fixed Price or to Make Offer? I'm intrested on all your feedback.
People are more likely to bid if they see a price than if it is set to make offer with no price. I have domains set at $100(+ make offer option enabled) and I get much more bids and some even bid much higher.
Set your price at a good starting point for negotiation. Low enough to attract decent interest but high enough to scare of the lowballers.
in answer to your question I have had over 200% increase in sales on make offer with a starting price.