I went ahead and broke the first rule of negotiation in that he who names a price first loses (as then it gives the other person a reference point.) I never considered selling the domain before. The buyer contacted me directly. They are a domain investor. I said $60K. They said $20K. And I said no thanks and left it at that. I got an offer like 10 years ago for $500 and about 7 years ago for $1000. The domain has high nostalgic value to me, but not business value except for possibly being worth more in the future. The website generates no traffic.
In my book, anyone worth their salt as far as negotiating skills isn't going to offer you their highest offer right off the bat. Also, although it's probably more rare these days with all the new TLDs, I'm sure many times in history, a domain has sold through a broker for $10X that was representing a company or person with deep pockets that would have paid $100X and the seller just had no idea.
So how do you "test the waters" to assess the true demand/current market value? Seems to me you auction it with a high reserve. Many sellers I think don't like to use auctions because they are making their money on high volume sales, so listing many domains that sell in the hundreds when many may not sell or not be profitable after fees makes the auction not make a lot of sense. And if you are trying to make a living selling many domains for $50-$500, then I'm sure these numbers of $60K and $20K I'm throwing out are very attractive to many that would say take the money and run. But for some people $1 is like $1,000 to others. It's all relative.
So what if you just want to double check you aren't being low balled and there's at least one other potential buyer willing to pay a lot more? Why change the website to have a for sale sign with a link to the Sedo auction, set a high reserve and contact all the domain owners of similar domain names to maximize exposure to potential interested parties? If it doesn't get bid up past the original buyer's initial offer, then yes, now you are in an awkward situation and the offer has a chance of being retracted and lowered. But I think that's a small chance given most likely the buyer is willing to pay more than their initial (unless they aren't a good negotiator) so they probably would still at least pay their initial offer. If they try to go lower I have no problem walking away as I don't really need to sell the domain, but I really don't need to keep it either.
The other thing is the auction would potentially flush out if the buyer is a fraud or not. Not that's a huge concern, except potential waste of my time, as I'd use someone like escrow.domains to handle the transaction. But I checked their own domain they use for their email and it's only an 7-month old domain so that seems a bit fishy.