What is the difference between the offerings in the "escort" vs "rub down" ads that I see on various sites?  Are they all offering the same things, just in a different listing? Or, are there completely different sets of rules and expectations for each category?  I assume that since many of the "rub down" ads offer lower donation expectations, tat there will be up selling involved when you make contact.  Is this correct? I know what I am looking for in a provider, I just do not want to make assumptions that are incorrect when meeting an advertiser that will embarrass either of us.

end with a hj/bj happy ending.  With an escort, you will probably get that as well, but also full service.  For full service with a rub-down provider, there very well might be additional charge for that.  If you want FS without having to deal with extra charges, just schedule an FS provider.  If all you want is a body rub with a happy ending, go that route.  Since you don't specify what you want, it's hard to say more.

Swim

So if an ad does not imply FS, then it would likely be a HJ.  I see some providers listed under both sections and others only in one section.  The one I am researching right now has excellent suggestive pictures, but seems pretty adamant that she is a massage therapist and I was wondering what the proper way to approach the contact would be.

that means she might be licensed by the state.  In that case, any kind of happy ending is doubtful.  She could lose her license.  In most, if not all, states, it is illegal to advertise for massage without a license.  That's why you see a lot of 'body rub down' ads.  If you just want a massage, go for her, but if you want more, there are plenty of others out there.  Just because she has excellent suggestive pictures is no guarantee you will get anything but a good massage.  I wouldn't push it in that case.  You didn't mention what site you found this provider on, but it sounds like BP, which in many areas is not the best place to look for providers.

Have you checked for reviews?  That would tell you what you might expect from this lady.  I suspect you have not done that.  You have 3 reviews, so you should have had at least some time as a VIP member to do the research.  If it has lapsed, pay for it, it's worth it in the long run.

Swim

with suggestive pictures.  So I suspect you are looking at a FBSM (Full Body Sensual Massage) practioner.  She may not use the term "Massage" if your jurisdiction requires a License for Massage.  Still this is what it implies.
A FBSM typically includes a HE...  a HJ.  I found that some FBSM stick to just that.  Others are agreeable to additional services but expect tips which would probably equal a FS provider.  These others sometimes will offer these services on the first meeting but I've also had others who only offer on repeat meetings, after they get to know you & that you're not LE.  
I enjoy FBSM providers when I'm in that mood...  also one that offers extras is among my favorites (UTR, sorry no reviews).  There are FS providers...  whose "massages" are generally not their best skill.

I would research this just as I would any provider...  but in the end, you don't know until you are behind closed doors.  I don't recommend you pursue this just to save money...  It would be unfair & you'll be disappointed if you want to get a FS provider at a bargain rate.  
skb