Site mentions "Free Lifetime Updates" but Codecanyon sales page says "6 months support from QuipCode" with a paid option to extend to 12 months. That seems somehow misleading and may potentially damage trust and cost customers.
I used to have other plugins that were sold directly, plus a couple in development which I may sell directly as well. When selling directly I have full control over the updates but through Codecanyon I do not have that benefit.
My preferred option would be to add support forever (helping people with the product, questions and so on) but actually limiting updates for a certain period, perhaps 1 year. That way I am paid for continually developing and improving the plugin but customer support is included always, which I think is important as a small business.