ZydoSEO - 9:35 pm on Jul 27, 2012 (gmt 0)
If you want to make sure you get paid before giving them access then use a service like Escrow dot com. They are very reputable. The service is simple to use.
I have no clue what you make per year on the site with AdSense, but sounds to me like you really don't want to let it go. So ask for some astronomical amount. I see people buying domains for $100k, $400k, and more all the time. If they want it then they will pay. Worse case... they walk and you're left with a site that still makes you money.
You have to think of not only how much revenue you make from the site, but also all of the money and time you've spent getting it to where it is at over the last 10 years.
You don't owe those people anything. If you sell, you're doing them a favor and are being inconvenienced into having to rebuild a new site. So make them compensate you appropriately.
And BTW, if you sell them the domain and move all of that content over to a new site, you are NOT going to be able to 301 redirect the old URLs to the corresponding new domain's URLs. You'll be wasting your time trying. As soon as they gain access to the site after payment, the first thing they are going to do is point that domain's DNS at their hosting account somewhere else... and POOF... any 301s you had in place just prior to selling will disappear. So you WILL be starting from scratch with zero back links.
And I would read the contract VERY closely if there is one (depends on size of company purchasing). Larger companies buying domains will often require a contract to spell out that they not only are buying the domain, but also all of the content, in which case you won't be able to use it on your new domain.