When I offered free hosting long ago, I had a TON of those clients! It was always funny to me that the free ones were the ones that expected the most! They think you're their web host, web designer, script installer/trouble shooter, SEO guy, and basic hand holder!
With paying clients you can expect some attitude sometimes, you cant please them all. I usually try to use the old "kill em with kindness" approach. The nicer you are, the more angry they get, but they definetly can't go postign on forums everywhere sayign "look how rude these guys are!"
Yuo just have to take the good with the bad. Maybe even suggest a coupel of sales that other web hosts are having,,lol