This question might look stupid coming from a member like me. I have never bought or sold a single site. I don't know how it's technically done. Are people giving out username and password to the ftp or what??
no, gather your stats together, take screenshots. Provide proof of revenue by taking screenshots, provide proof of age of the site, proof of PageRank, proof of number of pages listed in Google, proof of quantity of backlinks... provide proof of everything you can.
yeah, but if someone buys it.. how to transfer the site to the new owner? Imagine that you have a server with 100 sites and you sell one to a costumer. Should transfer it by only giving him the ftp info for the domains, should you switch server or how?
well, for the domain, if you use GoDaddy for example, you just transfer the domain to the buyers account and he changes dns servers to his hosting. And for transfering files, you can archive the whole site into .zip file and send it to the buyers email, or you could give the buyer ftp access.