Besides BBBJ and DATY I'd say eating ass is my favorite thing to do with a provider, I prefer it more than penetration actually. If the girl is hot and everything seems clean & appealing down there I just dive in. I recently had a session with a provider that wasn't down with it though. Her TER profile said yes on receiving and a couple reviews detailed DATO so I didn't think much of it. As soon as I barely licked her she recoiled and seemed pretty offended and was like "no, no no" etc and it kinda killed the vibe for a bit with her mood changing when everything was really good up until that point. I apologized and the session went on but still... Usually if I'm not sure whether or not a girl is cool with it I'll just kiss and lick around the general area and ask "is this ok?" kinda hinting at what I'm about to do and if they seem positive I just go for it and it's never been an issue. Maybe I should just straight up ask if I can lick their ass? It seems like it'd be weird asking that but idk.

I never do it on the first date because I don't want the girls to think I'm a slut.

I don't do DATO very often but I have not generally asked first, though it's probably a good idea.

them into the shower and wash their ass really well.  

I thoroughly enjoy this and ask if they mind getting on all 4s so I can eat their ass. One provider said no and said it wasn’t her thing so we moved onto other positions.

Before do sex Take a Shower and then do it. Yes buddy it is very weird But You ask her when you want to do anything because she also a human.

Someone I had seen before, I made an advance request.   So she was prepared for it.  
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I'd do it again if the lady desired it ... and is clean.  

Only kidding....
This really made me think. In all my years I've only DATO with one young lady. And as I reflect on how I initiated it, well she liked to rim me so I figured what's good for the goose is good for the gander, plus I really connected with her and I felt really comfortable with her.Now as to the how, as I was DATY, I slowly moved my way there, she didn't resist and the rest is history....I didn't ask to do it I just did it. Sorry but that's all I can add.

Maybe the provider in question had a bullet in the chamber and was just doing you a solid?

It's reasonable for you to expect MORE than a gander at her.  

I sometimes visit an Asian agency where the girls  will stick their tongue up your ass.  I politely decline.  The offer comes before you even get into bed.  These girls take a shower with you and try to stick their soapy fingers up your ass in the shower.   The first time this happened I jumped and asked what she was doing.  She explained she was prepping me.

...always make certain what the rules are...

“Pardon me, my dear, but do you prefer tongue or toilet paper?”

Especially regarding DATO and rimming.

upfront. No need to spoil the moment. Many times, simply declaring your intent to do something upfront can be a turnon (just leave her time to react). If the reaction is positive, go for it. If not, make a joke of it and move onto something you'll both enjoy. Consent can flow in the moment; it doesn't have to be (should not be) structured as a list of activities in an introductory email.

I just put my nose up in to it. If it smells good I just follow it. If the owner of the ass gets annoyed she just turns and snips at me. If that happens I run across the park and find another cute ass to sniff. Simple.  

"How do you initiate DATO?"

distilling this down to the basics.  Well done.  I probably don't know ALL the dog rules, so I might have to ask once in awhile.  Lol

Usually just sort of happens during 69..mutually..