I'm saying this as a data point for people just getting started who might be nervous about asking for payment up front. If we'll do it, I'm sure many other people will too. It's a reasonable request.
On the other hand, just so you know: we never ask for payment up front for our services, ever. That's because we'd almost never get it. Most companies with in-house finance and/or counsel aren't going to pay you anything in advance.
If I were freelancing, I'd ask for up-front payment, but I'd let the issue drop for any company I knew was large/established enough to pay me; if I was in a relationship with such a company and doubted the project really had legs, I'd just walk from the project.