I do offer deep throat and 99% of my clients ask before hand if they would like to push my head and for me to hold it. Ihave no problem with this, I make it clear to them that I can't breath during DT so they have to respect when I want to come up for air.
As for gagging, I provide this too. When you gag, your throat muscles massage the tip of their cock, this is one of the reasons why men like it. I am also sub, gagging is part of the excitement of bdsm for obvious reasons.
If you don't do DT, gagging and skull Fucking, then just discuss oral at the beginning of the booking to make your boundaries clear.
Now, lol, the thing that annoys me, is when a client wants you gagging to the point of wretching and bring up!
I had a client do this and encourage this the other week, luckily I had an empty stomach! Why on earth he hadn't explained his fetish and ask before the booking piss's me off! After I explained I don't like that he kept pushing me to achieve it. Fucking boundary pushers! Should of kicked him out, but I didn't, thought Fuck it, I'll give it ago, I'll try most things once. But no, no no no! Didn't enjoy being covered in my own spit , eugh! Saved as messy gross guy and blocked! Haha xox