When you hire someone, you have certain responsibilities you have to live up to. Especially when you’re working on a creative endeavor. If you have the answers, you shouldn’t have to be chased down in order to be asked questions.
As an editor with something of a name I’ve managed to make for myself, I ask for some form of payment upfront when working for a client. Not the entire thing, because that’s not fair, but some form of payment. This protects me from my client, and it protects my client from me.
Protecting me from my client: I generally don’t know the people who hire me from Joe off the street. I don’t know if they’ll take the work I do for them and then run off with it. It hasn’t happened (yet), and with all the horror stories out there, I do what I can to mitigate any damages. Asking for some of the payment upfront helps to mitigate that.
(And all kinds of things can happen when it comes to editing: you could edit the entire book and the creator just doesn’t pay you; you could edit the entire book and the creator doesn’t like what you have to say, so they don’t pay you; the creator is slow to pay for the work done on the script and you have to hound them; mix and match any of these scenarios, or make up your own.)
Protecting my client from me: Like anyone, I can get lazy when I’m paid for the entire project upfront. Not paying me the entire thing gives me incentive to do the work. Since I have made a small name for myself, it’s pretty easy to ruin that by not doing the work that was paid for. If I ruin my name, I can’t get more work. (Well, it will be a challenge to.) If I am paid but don’t do the work, then it is on me to rectify the situation. I am much easier to smear than Joe off the street.
There have been times when I’ve been fully paid in advance, and then the creator disappears after I do the work. I’ve done my part to contact them, but I’m not going to go out of my way to track them down for work owed. That isn’t my job. I’ve done my part, so it is now up to the creator to do theirs.
Disappearing is never a good thing. Live up to your responsibilities as the hiring party. Otherwise, you could be wasting your money.