Castion,
I love how you say take it and run!!!. This is a company in Europe, they contacted me via LinkedIn. What do you mean by end user? I know that can be applied to different scenarios.
Thanks
Usually we distinguish between two buyer types in the domain industry. Resellers and end users.
Resellers are the people that buy domain names as a (more or less) passive investment to sell for profit.
End users are the people that buy domains to make use of them. To create a personal website (lowest tier), all the way to large corporations buying a new URL for their new projects.
End users pay 10-100x more for a domain name than resellers do. Resellers will try to establish a floor or liquid value and acquire the domain below that price. This is usually based on stats like you mention.
End users will use their own business metrics to establish the value of the name to their company.
Frankly I think that 20K is more than a fair offer. If its their opening offer you can try and see if you can extract an extra 10-30% from them, but I seriously doubt you will have an easy time finding anything comparable from another bidder.
So to reiterate... Take the money and run!