Tips for setting boundaries with customers who email a lot?

Hi - got any ideas on dealing with those rare 1-in-300 customers who start sending weekly email questions to things that are already clearly answered on your sites' FAQ areas? You probably know what I mean, if you have a lot of customers. Gracefully set boundaries, deliver superb service, but for rare "constant contactors", then what?

For example many places now charge support ticket services, eg send in a question and it's $_ a month or whatever for the service plan; I dont want to have to do that, but obviously a lot of others are doing that, to stem the tide of questions already answered in FAQs.

What would you do, about the new customer who, after a couple initial emails, then sends in once-a-week emails with questions that are already answered? If I was running a $10k/year platinum mastermind, then a lot of contact's expected and fine, but for say a sub 1k info product, how many email questions are too many? I politely refer them to the right resource areas, but some people just seem to think that buying a product entitles them to a lot of email contact. I always go for answering all emails, quickly and personally, to be professional and helpful, but it often makes my 16 hour days turn into 18 hour days.