Has anyone had any experience with negotiating the sale of a domain that they own?

I've been approached by a U.S. Company acting as a third party (they check out okay) to buy a .co.uk domain that I own.

I don't want to list the domain name but it relates to a multi-million dollar global brand. So I have a pretty good idea of who they are acting on behalf of.

I've been too busy to respond to emails and a member of staff from the company did call me (Whois lookup). Told them I was busy and that I'll get back to them.

Anyway, after a couple of weeks silence I receive an email offering a several hundred quid. It's a fantastic return on a 5 quid per year investment but I strongly suspect this initial offer is just to test the waters or a low-ball first offer.

No lawyers involved and I can only suspect it is because I obtained the domain prior to any trademark, plus I am in fact hosting some sort of static page (not offering it up for sale, but actually using it).

My research on domain valuation simply throws up 'how much does the company value its brand?'.

Anyway, has anyone here had dealings with a similar company, looking to buy your domain? How did you negotiate the deal? Any advice?

Cheers.