It isn't worth much. No serious person would EVER EVER EVER develop a site on a .co without owning the dotcom. That is not really debatable. If you were offered $100, then you can counter with whatever you want. With a name like this, if you counter at 3K and the person never responds, you can start working your way down to where you might end up getting close to his initial offer. There are times where you can counter offer and scare the buyer away, and it can happen to where the buyer will no longer want it at any price, but with this name, since they contacted out of the blue, you can probably take a shot at a lucky price without blowing the deal. If they want it for a few hundred and you counter with thousands, my guess is that they will still want it at a few hundred after they hear about your outrageous demand.
Also, anybody ever spends 10 seconds talking about Estibot has just wasted 10 seconds. It is a very amateurish thing to do. I have never once in my life EVER run a name that I owned or wanted to buy through any type of Estibot-ish type site. You might as well have a computer tell you if the girl walking down the street is good looking or not. Just plug in some info and get your answer.
There was a name that someone posted the other day that had me clicking on an Estibot link for maybe the second or third time ever, just to see how unreasonable it was. He posted it here in the appraisal section. The Estibot appraisal was for 231K. I would rather have $200 in cash than the name he listed. I would bet my right arm that those who run the Estibot site would not give him 2.3K for the name right now. So, that means that they can appraise a name at 231K and yet not be willing to buy the name for even one percent of the appraisal.
So tell me why anyone on the planet would care about Estibot? I don't get it.