The domainer version of this question would be: should you try to seal the deal with the first end user who makes you a reasonable offer or wait for more generous end users to come along?
At the end of the day, I think it’s all a matter of trying to assess the likelihood of receiving a better offer for the domain in question.
For example, let’s assume you own a CVCV dot com and a domainer offers you an amount which basically represents more or less the reseller market value of the domain at that point in time.
In that case, the likelihood of receiving a better offer from someone else is high.
CVCV dot coms are highly liquid domains which can relatively easily be moved at market value, so there are no reasons to be excited if someone puts such an offer on the table.
But what if you were to receive an offer for a domain that’s considerably less liquid?
Let’s face it: for a lot of domains, the offer you just received may very well end up being the last and as opposed to short domains, lots of other domain categories are considerably harder to liquidate.
Can they be sold on the reseller market?
Yes but unlike with short domains (for which it’s relatively easy to obtain the current market value), you will most likely have to settle for prices that aren’t exactly worth writing home about
My advice would be this: whenever you have a reasonable yet firm final offer from an end user, ask yourself what the likelihood of receiving a similar or higher offer is and take that answer into consideration before deciding what to do next. There are no “one size fits all” solutions in my opinion and therefore, decisions should be made on a case by case basis.