If you have been in a coma the past few weeks (or longer) you may not have seen all the news stories about inappropriate sexual behavior. Well, you can relax. I am NOT going to talk about any of those stories. What I am going to talk about is something more relevant to mongering: Appropriate and inappropriate behavior toward working girls. 
Anything that is legal and consensual is basically ‘appropriate.’ The key word here is consensual. There are men who don’t seem to realize that when a woman consents to have sex for money, it doesn’t mean she has agreed to do anything and everything. Don’t expect her to do everything you see in those triple X videos you watch.
There are a lot of kinks and fetishes in this world. From what I have seen, there are a few who will consent almost anything. But once again, I use the word ‘consent.’ Just because some video producer has found someone willing to be humiliated or abused on camera doesn’t mean YOUR date of the evening will be willing. Almost surely she WILL NOT.
Asking is permissible, but depending on what you ask for, don’t be surprised if she says no, or reacts with revulsion or even fear, depending on your request. Also keep in mind that there are some kinky things that a girl would be willing to do TO YOU, but not at all willing to let you do TO HER.
To take S and M as an example, I live in a place where advertising sexual services is totally legal and uncensored. In browsing these ads, I come across a fair number of women offering ‘dominacion.’ Just in Medellin for ads posted today, I found six separate chicas offering domination. Not my cup of tea, but different strokes for different folks. But I have yet to see ads by women wanting to be humiliated. Such women may exist, but are probably happily married to sadists.
But to return to the main point, appropriate behavior with a sex worker is only what she consents to. Anything beyond that is NOT appropriate and the mark of a jerk.
We can see the outside, at least the part not covered by clothing. For that matter, clothing can tell us something too, although it can often put a sexy front on a cold fish. But what goes on inside someone, a working girl, for example, can only be imagined. Over time, actions and words can fill in parts someone’s vast uncharted inner life, but only parts. 
Thanks to Google Translate and similar apps, the interview process has never been easier. Unfortunately, too many mongers don’t take advantage of available technology, or, even worse, don’t put any thought into the interview, not realizing how important it can be in choosing a suitable short-term lover.
On the purely technical side, assuming you are not fluent in the girl’s language, there are apps that make it easy to do rough translations. I have an Android smart phone and I installed Google translate. I suspect there is an Apple equivalent. I can actually speak English into my phone, and it will SPEAK the Spanish translation back. It’s not totally perfect but it’s better than I would expect. It may not translate slang and it MAY have a problem with a thick Brooklyn accent, but overall it’s amazing. It works very well in person even if it’s only on your phone. You can change the direction of the translation to where it translates the girl’s Spanish back into English for you, then switch directions again to talk to her, etc. etc.