READ her reviews. As many of them as you can. Including the Juicy Details (yep, that requires VIP). If you find something odd about a review, and it's from a hobbyist with a strong review history, you might PM him and ask courteously for more information (do this with your handle, not an alias, and if you don't have a review history--which you don't yet--then mention you're a newbie).

Another thing to do is, if the provider has a web site with photos, use google image search et. al. to see if the photos are from another source.

Personally, I don't consider not having a web site a big deal, if the provider is on a site like P411 and has a good review history. Two of my favorite providers don't have a web site.

not just to see if I like her look (and it's definately different strokes for different folks)...  I've found if the same 1 oe 2 hot pictures are repeated everywhere, they may be all she has.  In one case I found they were 10 years old, she now was 20# heavier & sported full body art.  
I look for a variety of poses, variety of dress & undress.  Need not be totally explicit but taken in total I want to pretty much know what she looks like standing naked.  I prefer a gal who might rotate 6-12 pictures among her ads & all look like her.  If some of the pictures seem to be of another, that's a turn off.  

++  I read many full reviews, looking to see how consistant she is in services.  It's not unusual for a gal to offer BBBJ in early reports & then to become CBJ.  

I look for more reviews and at least some experienced reviewers reporting a quality experience.  I look hard at the most recent reviews for warning signs of burn out.

I would suggest several pages of reviews going back a couple years or more.

I can't stress how important it is to pm her reviewers. You get much more honest info that way.  

Read her posts as that will tell you more about personality and any BSC behavior you may want to avoid or at least minimize.

1)  yes
2)  yes, reviews over time meaning not all in the last month or two
3)  not a biggie for me
4)  maybe
5)  Read the juicy details in her reviews and PM some of the reviewers to get additional info

Sometimes providers start out with CBJ on the menu and then decide to offer BBBJ.

#1 and #2 are the important ones (though you could bump up #1 to 10 reviews or so to be even safer - though honestly, if she had 5 reviews from ALL very well-established reviewers - guys who have lots of reviews of VERY reputable ladies - then I think you are fine).

As I'm sure you implied, but others have also explicitly instructed you to do - read the reviews.
One VERY important thing to me is looking for guy's comparisons of her photos to how she looked in person.
A guy can say a woman is beautiful, but that is very subjective.  However when he compares how she looked in person to her photos (same, older, heavier, etc.) that is much more objective and helpful.

Beyond that, use your own best judgement after reading the reviews, as a lot of this stuff is subjective and I'm sure you have an idea of the type of lady, service, and personality you are looking for (oh, and also, I suggest you DON'T let really really hot photos persuade you to give a girl a shot, even if her reviews aren't good - a strong consensus is usually right, and it's not like you will be the one great guy to magically bring out the best in her!).

I discount a gals first review until such time as the review is confrmed by several later reviewers.  While some first reviews are accurate, others have major discrepancies with later reviews.  I will give much more credibility to first reviews with experienced reviewers whose opinions I have come to trust.  

For Newbies & the risk adverse (I mostly put myself in the latter catagory), I suggest a minumum of 10 reviews with at least some by experienced reviewers.  This has proven a safe combination for me.  If there are pages of reviews, I focus on the most recent page...  what she offers now.    

Some reviews don't give much of use to me.  Comparisons to her pictures is useful.  

I look for certain services even if I don't necessarily partake each time because it shows a willingness to please.   I have seems gals who might have limits like FBSM which I enjoy...  but if I'm looking for FS I want a BBBJ even if I don't finish that way.  I don't have an agenda...   I like to let a session flow

Thanks for the great feedback everyone--this is helpful (especially quantifying how many reviews can be considered "safe").
To clarify, most of my motivation for doing homework is to avoid a sting/LE.  A bad session is one thing, a sting is quite another.  Any other tips/boxes to check when doing your own "screening" has a hobbyist?