Many web designers will try and tie you into a contract for your website updates. This can sometimes be an expensive ongoing cost and a lot of time once your website has been launched many people don’t update as frequently as they should.
I would love to charge retainers for updates as it would be a useful source of income, but I always had this niggling feeling I was conning people out of money, as in some months clients do not ask for any updates.
The fairest way I feel was to just charge for updates as and when needed, I do this for all my clients.