If I'm the seller I would prefer to throw out a number. That way you can simply pad the starting point, coming down in price is much easier than going up.
That's great until the person you're selling to immediately jumps on that. At this point, you are left wondering, "Gee, was my offer that good? Was it too low? I wonder what he was expecting to pay. Damn, I could have made 20% more had he made the first offer." Same goes the other way around. The trick is to have both people negotiating to leave feeling as if they won. In your case, you will leave feeling as if you lost.
I'm not convinced that that's a good enough reason not to do it.
If you are that much more concerned about getting the best possible price (or whatever) vs. getting a set number you actually want, then you should go into the negotiation with enough information to already know what the best possible price should be.
If you feel like you lost, your initial offer wasn't high enough.
I once suggested a salary range from [thrilling for me] to [unbelievable] and was offered the high number. I never felt like I "lost" -- until of course a year later when we were all laid off in early 2001. Ah, the "dot-com era."
I suppose some people will always be haunted by suspicions their deal could have been better. But for me, people instantly accepting my high offer is not going to be a lifelong regret.
