http://Flippa.com does a great job simplifying the "buy a whole business on the web" process.
There are 2 buttons, "buy website" and "sell website" that split traffic accordingly and make things happen.
They also did a usability test with https://UsabilityHub.com and made the results public, which you can see here:
https://usabilityhub.com/tests/c942c855fa6/results/fbee3843a15f