I loathe it when sellers say "make an offer". My standard reponse is either $1 or $10. They will then usually get offended, to which I respond, "Hey, you said to make an offer, so I did."
The subject has been discussed before and I will state my opinion again.
The SELLER is the one that has the name and THEY should establish the going rate. You do not go into a grocery store having to make an offer on your food do you? Nope. When you go car shopping, prices are put on the automobiles to give a starting point. I will rarely say make an offer for a domain name. On the rare occasion where I do say that, if the interested party presses, I always will state an asking / target price.
The sellers line of thinking is "What if I sell for $100 and they buyer was willing to pay $1000?"
My response: If you were willing to sell for $100 and take a profit in the first place, then you are getting greedy by making the seller go first. Nothing wrong with trying to get $1000 for the name, but say that up front. It would save a lot of time. Additionally, if you are unsure of the value of a domain name, then you need to do more research on it before giving an asking price.
The only caveat to my opinion is if you appraoch a domain name owner who has not listed the name for sale. He is not actively trying to sell the domain name, so the BUYER should start in that instance. If the seller initiates the sale, then they should ALWAYS go first.
My DNF 4 bux worth.
-Bob