This guy is bad candy.  He used the n-word repeatedly with me as well. I got the impression that he was just saying it to get a rise out of me, so I ignored him. He upped the ante and started talking about blackmailing escorts/dommes who don't do what he wants.  He also talked about how he has an enormous wolfhound that attacks people; this somehow felt threatening, although he didn't say anything that made me feel in immediate danger.   Definitely one to avoid. 

Beware also of the £10 sandwich, i.e. tenners that hade twenties on the outside, and the correct number of notes as though you'd been paid in twenties.  This doesn't happen often, but is worth watching out for. 

This puts me in mind of the episode of My Name is Earl where Patty the Daytime Hooker has sex in exchange for hamburgers

I would add "Having Sex with Ugly People" to the list.  While hygeine is an absolute minimum and should be expected, the fact is that many clients are unnattractive.  You will get the occasional hottie, but you do have to ask yourself if having sex with someone you aren't attracted to is going to be a problem.

"Awkwardness" is another issue.  Your client may behave perfectly acceptably but there is no real click between you.  This can leave you feeling horrible.  Additionally, many polite and clean clients are shy and inexperienced and may be poor communicators.  This can feel embarrassing and awkward, and you will walk away from the booking wondering whether you can do this job.  If you can ignore or accept these feeling, then you'll be fine, but if not, reconsider entering the profession. 

I'm allergic to sulphur dioxide and I've been feeling pretty ill for the part few days.  I've not seen much in the way of ash though. 

Some clients will ONLY go to girls who do oral with, some only go to girls who do it without.  For others it doesn't matter one way or the other.

From the medical side of things, not even medical experts agree on whether or not OWO is a serious health risk.

Therefore the only  reason, and it is a VERY good reason, for refusing to do OWO is because you don't want to. 

Fetish clients are the best and worst customers. They are either total timewasters or exceedingly loyal.  As far as uniforms/dressing up goes, tell them that you will change when they have arrived and paid, and that this will not eat into their time.  Serious ones will show up, timewasters will hang up.  If the call is going to be more than 5 minutes, ask them to email you.  I'd reserve watersports for people who have seen you before, or for longer bookings where you can "prepare" early in the booking, to avoid the types who want you to drink a gallon while waiting for them to arrive. 

Did you try just touching his forhead lightly, or maybe turning him a little?  This works pretty well, not that I'd know ANYTHING about such things!