As you approach the sensitive area, rub just outside of the labia very lightly and gently as you keep an eye on her face.

If it is all smiles, then encroach ever so slightly and continue to watch her face for a reaction.

She will signal with her face whether your venture is welcomed or not.  Starting off very delicately and spending a lot of time preparing her so that she gets moist and then wet is very important.  

She is checking you out to see if you are being careful and respectful.  If her expression is rather neutral, you could ask simply if she is OK with how you are proceeding.  Hopefully you'll get a nod.

I've been in these situations many times and have always had some degree of success, though many gals have admonished me not to go inside, or to remain on the periphery of their vulvas.

It's a fun dance to do.

Just a curious question regarding a mutual massage with a provider. When you are getting a body rub/massage and she offers mutual massage (which I couldn't turn down if no upsell) she'll turn over after a fashion on her back and present all the fun places to rub. I know it's very commonplace to massage and rub her breasts, stomach, thighs and legs but some may allow massaging and touching of her vagina. Is this common?  Are there any clues to her allowing it other than her keeping her legs spread pretty far apart?  I've had a provider before keep her legs spread wide open but I was terrified to touch b/c I didn't want to end our fun abruptly nor did I want to ask the awkward question. Jut looking for a little insight. Any replies would be helpful.

Several years ago I was getting a massage from a gal who was working in a residential AMP but only offered limited services-no two-way massage.  We seemed to be getting along and she was going at me pretty good.  No FS or BJ but she took her top off and invited me to fondle her breasts a bit.  As I did this I noticed that her panties were soaking wet right in the center of her crotch.  I moved my hand lower and started to rub her belly in growing circular motions.  Within a minute or so of this she pulled her panties aside and allowed my hand to roam where the wet spot was.  I gently rubber her clit with my thumb while moving my fingers...first one then another inside her.  She started moaning and eventually got so loud that the guy in charge downstairs yelled up to make sure she was alright!  She yelled back down that she was fine and then we finished each other off as she collapsed on me.  Best hand job I've ever had.  Unfortunately she left town and the place got raided and shut down before she made it back to town.  I'll never forget that night even though I didn't get so much as a BJ from this woman.

It's not a mystery and is really a "do your homework" question. Read her reviews.  They will say if she offers massage.  They will also say if she allows FIV. That's really all you need to know, but then try reading The Juicy Details.  All will be revealed.  Assuming you've got VIP.  If you don't get it, you need it.
Another thing good about VIP is you get PM privileges so you can PM her reviewers for more detail.

to her honey pot.  As I lower my head to get real close I say, "May I?".  The response is usually. "Oh please".  Most providers enjoy a good DATY session.  I do not use lotion "down there" or on her breasts as I prefer to use my tongue.

Should be used on your experience with her. Don't forget to show her action and explore. There may be something she likes and she wants u to find it or she may not even be aware if its something new... YMMV... Personalize your experience while being attentive communication weather body language or spoken is key. Good is good but no limit it only gets better..  
If you arent good at reading body language dont be afraid to speak up. Just a little at the least

Thanks everyone. I know it's a YMMV situation w every girl. It just get confusing or awkward when she presents herself in a certain way and then has strict rules which are her perogative and her own mileage to give away. It just seems like asking even very sensually, is awkward or me and I've been hobbying it over 10 years now.