You live in a small town.
It pains me to write this one, since I grew up in a small town, and I would be pissed if I read this. But you really need access to several temp agencies to make it work. How many? Hard to say for sure. I would say 5 at a bare minimum, and 10 is better. There's probably more around than you think -- Seattle proper (not counting the rest of the massive metro area) has 90.
You have no experience whatsoever.
Most agencies will want you to have at least a year of doing something. Snazzier places will want two or three. If you've never worked before or have only worked in McDonald's, suffer through a year of being a full-time office bitch. Get a reference and an item for your resume.
You require the security of knowing where your next paycheck is coming from.
Temping is a lot like freelancing this way. You will have dry spells. You don't know from month to month where you're going to be or if you're going to be working for sure. If you freak out at the very idea of this, or if you have nothing resembling a savings account (or a puddle of money in the bottom of your checking account that you never really dig into), you are probably better off with permanent work.
You require benefits.
Again, this is like freelancing. You're on your own in terms of benefits. (Sometimes. Laws vary by state -- in Washington, if you work at once place for six months or longer, the company you work at must provide benefits.)
You are not a good worker.
Be honest with yourself. I can't say I blame you if you don't bother doing the best job you can on soul-draining low-paying office work. But nonetheless, if you can't bring yourself to do excellent work even on silly little tasks, you will not get great evaluations from the companies you work at. And without good evaluations, you have no hope of sustaining steady employment.
You want a lot of money.
Okay, well, this one's a no-brainer. Most people want a lot of money. The question is more how much you want it. The real payoff of temping is time, not money. Don't go into this just for the money.
The nature of a job is trading free time for money. You can adjust how much you're giving and getting, and it's up to you to decide how much of one you want to give up. For me, it is 100% true that money does not buy happiness. I tried that, and it didn't work.
If you have expensive hobbies, an expensive lifestyle you don't want to give up, or if you're saving for something big like a trip or an investment, a permanent job is probably a better choice.