So, this may seem like a rather silly question, but how would one go about TOFTT in the safest manner possible?

While I have seen quite a few providers (which reminds me, I'm quite behind on reviews...shh...), I've always used the TER mantra of 'research, research, research'.

Now clearly, someone must have TOFTT at some point for a 1st review to be posted. But if a number doesn't turn up any info, the provider is able to provide info that matches one's ad, and the ad is written with some vague semblance of correct sentence structure, what other rules of thumb should I use when TOFTT?

Much obliged.

I'd suggest 2 reviews... both good & agreeing on the basics.  
If I were to select an unreviewed lady, she'd still have a web site & still screen.
skb

Call me cautious, but...
I want to see that she's established, i.e., reviews or ads posted over a period of at least three or four months. In the alternative, I'll go with an agency, established over time with consistently good provider reviews.
In a way we're all like penguins crowded on a ledge overlooking the water, none of them wanting to be the first to jump in.  I thank those of you who do test the waters first but I'm not going to join you until I know it's safe.

when there are so many attractive and well reviewed ladies out there. However, the guys I've seen who have been successful, go with agencies that they frequent. The agency Booker let's them know there's a new girl in town, and they show up knocking on her door. I seldom see negative reviews written by them.

It's quite silly why I would even bother TOFTT considering that there are, as I and everyone who has replied know, plenty of well reviewed agencies and indies. I guess I just envy those who risk their necks to rate a gal for the first time.
But for now, I'll be thinking with the big head, not the little head.

either hobbyist who are on boards where you can contact them about her, or other escorts who have reviews.

Other than that, you are pretty much sticking your neck way out.  The odds favor you, but still, there is a risk there.

Also, see if she is willing to banter back and forth in emails until you can a sense of security with her.  You have to know the reliability of your own BS alarms.

you are not ready to TOFTT.