does using a verification service (ex. p411 or rs2k) help to avoid trouble with LE? i.e. would a LE post as a provider on p411 or rs2k?

The chances of LE being a well reviewed provider on a verification site are slim but LE is every where, if you have access so do they.  They have managed to take over client accounts in the past when guys get busted and they don't know their rights and don't keep their mouths shut.

In Denver, the Mid-West and the South, LE has busted providers who had P411 accounts and then used them to entice Johns.  P411 terminated the accounts as soon as they found out.
I am pretty sure this description is accurate but anyone who can clarify this should weigh in.

From what I understand (at least in the Denver cases) it was actually the other way around. Cops were setting up P411 profiles, then having coffee dates with some newbie-friendly ladies who then gave them Okays. Armed with several Okays, they then used that to schedule actual dates (not just coffee or whatever) with other ladies, who were then busted.  

In Denver, it was being used to bust escorts, not clients. I heard p411 nipped it in the bud. I sure hope they did. Seems like a waste of resources for the police. Why focus on activities between two consenting adults when they can be focusing on real crime such as murders?

...the story with ""Previous investigations nationally have shown links to this type of website may involve human trafficking violations"  
http://www.denverpost.com/ci_23479062/prostitution-bust-nets-22-denver-metro-area

As per why cops do what they are doing is a whole other topic. This is a backward country in terms of legislation on drugs and adult industry, first off. As per the cops, busting straight folks who work for a living and pay their own ways is the easiest law "enforcement" they can do, besides hanging out around dunkin donuts.

All criminal activity is real crime, according to law.

P411, I do know, has their servers outside the US where prostitution is legal, as I assume, do the other verification sites.
As also mentioned, in this enterprise there is always risk, so we all must be constantly vigilant.

What are the chances LE could infiltrate this site? Totally new to this, the ladies that I am thinking of seeing are only top tier -- have multiple reviews over many months by reviewers who have reviewed multiple other ladies. Is there a way to fake that?  

as long as you take reasonable safeguards, see only well reviewed ladies and if there is no reason that someone would go the extra mile just to "get you", you should be perfectly safe.

For an example, I am only "reasonably" safe at most, as I don't have a wife, job, or anything else that I could lose by getting busted, but even just being "reasonably" cautious I have seen literally thousands of different providers over 4+ decades without having ever been arrested for it. Hopefully that, and the fact that the overwhelming majority of the other mongers here have also done this for years without any major problems will allow you to sleep at night.

LE is on this and every review site. If they want to get someone they will.  
There have been cases when providers were flipped when they were busted and faced much more serious charges than simple prostitution but it's rare. Their typical MO is to put up a BP ad with tempting pictures to lure you many other guys into their net, the biggest bang for the buck comes from volume not going after one guy.  
 Indy providers get in trouble most often when something happens to generate a complaint from neighbors. Bigger headlines can be made and more serious charges had by taking down an agency than a lone provider.
 This is an illegal activity and the risks are real

Think about this for a minute, what screening did you go through to join this site? Your payment is not screening. LE has been on here for years, they are also on every other site you can find.

My main question is . . . If a lady has multiple reviews from reviewers who have reviewed multiple others, is she therefore legit?

and that is saying something too.

Nothing is ever 100%, but consider this for a moment:

Even before I started using TER about 10 years ago, I saw over a 100 gals over the course of 30 years, most of them from ads in local weekly newspapers.  If ever a guy should have gotten busted, is was I.

But, I didn't and the reason isn't on account of me being so wonderful and cautious, but rather for the same reason I'll never win the lottery:  The law of averages.  

Consider the incredible number of people who hobby every day and then consider how few resources LE has to deal with that and you'll see why.

I'm not suggesting that people should just go willy-nilly and call any old number on Backpage, but rather that people who do stick to well reviewed providers as you suggest should not worry about getting busted by LE, and spend more time covering your tracks with the SO.

That's where I screwed up, twice, in fact.

Legit, as in being a provider? Of course a lady with what you mentioned is legit so are the majority of ladies on BP and ever other site.