After you hand the site off to the client change the ownership of all the files in their path. To do this ssh into your server as root and change directory to the root install path for your client’s site e.g. cd /var/www/vhosts/site.com/httpdocs/
<– Media Temple’s setup. Then run
chown -Rf username:group *
If you happen to be using a Media Temple VPS it would look something like this:
chown -Rf username:psacln *
If you don’t know the root path of your server a quick an easy way to find it is to open up any one of your php files in your WP install, like the header.php and use
echo $_SERVER['DOCUMENT_ROOT'];
Note that most of the time this won’t hurt anything, but since you are logging in as the root user, just like any other command use with caution.