One lesson I learned doing translation is that it's best to consider even completed jobs as incomplete. As with any art, perfection is impossible, and if you're doing something that demands creativity, the job is never done. I don't mean this in a negative sense at all, I mean it in a 'you can always improve' way.

If you're taking on a creative job, especially something like translation or web design, understand that your customer is going to come back to you for updates and revisions. Include this in your quote. Tell them upfront that any and all revisions will either be included in the cost, or what your fees are once the initial job is done.

In that regard, it's better to not consider the job done, well, at all really. By doing this, you gain the trust of your client, which is often more valuable than the time it takes to do the updates they ask. In turn, you can build better clientele too.