Once we've received your file we need a commitment from you that you will not edit it again until you receive the edited version back from us, even if you think you have a million brilliant ideas to improve it, or you find 1000 errors in it yourself. When you send us one version of a file one day and an edited version of it another we have to charge you (at an hourly rate) for any time that we have already spent editing your first version. Why? Well, we simply cannot merge the two edits (yours and ours)