As stated elsewhere, the only excuses a client has for posting a review against the provider's wishes are
1/  false advertising
2/  health or hygiene issues.

Period.

And in those cases I would feel it appropriate to advise the provider as early in the encounter as possible - immediately upon making the decision, that it is appropriate to do so.

Anent the presence of one of the two issues above, if you tell the provider you will not post a review, then DON'T.

Superman:  "I never lie."

Bunch of good questions and the properly ethical answers are not all that clear.

1/  If a provider does not want to be reviewed at all that should be respected UNLESS:
   a/  The encounter was a total rip-off (no-show, extra $$$ requested when full service was supposed to be included in the stated charge, etc.)
   b/  The photo/description/service are not as promised/advertised.  Inaccurate photos/bait_and_switch immediately allow the reviewer complete freedom to report on the encounter.  I respect the right of the provider to their privacy.  I also believe in truth in advertising.  Lies should be exposed.

2/  If the provider accepts being reviewed:
   a/  YMMV issues and personal taste issues should be clear.  I don't set great store by Robert Christgau's music reviews because my tastes and aesthetic values are different.  Also, frankly, I am not particularly physically attractive.  It would be unfair to hold that against a provider.
   b/  Detailed physical descriptions of the activity involved may be tittilating to the reader, but are frankly less useful than opinions on the ambience, the attitude of the provider, and the ratio of promise to fulfillment.  
   c/  Since these are key issues to the general punter, unless there is a strong objection from the provider to dealing with the following issues in a review, it is OK to report on whether or not BBBJ, DATY (of particular importance to your humble scribe,) DFK (nearly as important to moi,) or Greek are on the menu.  But it must be clear that this relates to the YMMV issue.  Face it (so to speak  if you were a provider, would you be enthusiastic about either DFK or DATY with a client with bleeding gums???  Just like Jerry Seinfeld says, we should all regularly floss and if we don't, we have no one to blame but ourselves if providers, SO's, coworkers, etc. balk.
   d/  Likewise, hygiene issues with the provider fall under part 1/ above where reporting problems supercedes the right of privacy due the provider.  Since Mel Gibson is an actor, if he makes (as he has pretty much done since abandoning the Mad Max character) a wretched film we have every right to advise people of that.
   e/  Complicated???  Yup.  It all comes down to respect.  If you get respect from the provider you are ethically responsible for reciprocating.  This, however, is a two-way street.  The absence of basic respect from a provider, so long as the YMMV issue is consciously acknowledged, may be reported.  This ain't as hard as it sounds.  As a reader, it is fairly easy to differentiate between reviews that report on real issues and reviews where the punter is focussed on his cocksmanship rather than the encounter.

I don't think their marriage will last.

At least make sure he takes a shower first.

did he have sex in it?   If so, I will rent it.  I LOVE Brad Pitt!   Second only to David Duchovny.