Hi. What's the best way to say to an end user that his counteroffer is low, but you may be willing to sell the domain for his price if no one else replies with a better one (I emailed a bunch of potential buyers).
Why do you inform that his/her is the only one interested
Take time and don't be afraid!
You can answer: " I appreciated your offer, but we are not in the right ball park." Then, make an offer more affordable and so on ...
I recently had an end user make an offer under $150 for a ten-year old .COM. While I was tempted to respond I decided to not waste my time because from prior experience, the initial offer is a good indication of how high they are willing to go and I am not interested in selling that particular domain for $XXX. But there are cases where lowball offers have been negotiated to five figures. Each case is unique.