In almost all cases the type of bug for which you'd have to fix would be fixed by then; and besides, as part of the "sale" you advertise free updates and fixes for one year.
So I'm interested in how, technically more than anything, you will support people. Because if you are just going to fix individual problems, that means a lot of branching and more code management.
Maybe the easiest answer is to just give those people free upgrades? So I'm interested in how you are handling this. I asked myself exactly this question eight years ago and came up with my different answer, so I'm interested as to how you came up on your side.