One of the hardest things for a writer to do is recover a payment from a client. If you accept a job, then don't get paid for it, there isn't much you can do. Many times the jobs are Internet based and all interaction is done by e-mail.
The client can be in another state or even another country and you're not going to spend money on a lawyer or collection agency especially if the fee $100 or less. This used to happen to me occasionally and just considered it the cost of doing business.
In fact, many times beginning writers feel like they have no recourse for clients that don't pay except to say you won't work for them anymore. (I have quite a list.) A while back I started requiring a 50-percent deposit from first-time clients.
This served several purposes. It showed them that I was serious about writing and that I'm not to be trifled with. If they send the money, then they have a financial investment in the project and if they don't pay, I at least have half the money.
If they balk, then they probably weren't going to pay me to begin with, so screw them and good luck with another writer. There are some writers that required full payment upfront, but I'm not comfortable with that.
Ultimately, it's your choice, but one way or the other get something upfront. Short projects or long projects doesn't matter. You deserve to have something up front as a good faith payment. It's standard business.