Although I am not a provider, an essential skill that a professional provider should possess is the ability to service nearly any client they choose to visit with regardless of some of the negative attributes mentioned in your question.

I remember reading a comment about a young man telling a friend in a crowded bar that he envied the positive side (money & plentiful sex) of providing. He felt that he would enjoy the line of work (being a male prostitute). His friend quickly challenged him to pick out the most unattractive woman in the bar and envision himself being able to service the woman. That reality is what he would need to come to grips with if he truly desired to enter the pleasure business.

In any case, the coping mechanism that most providers possess is the ability to focus on one positive attribute of a hobbyists' appearance. If they can identify something positive, it is much easier for them to engage themselves into provider mode for the session.

But if they're smokers, drinkers  have bad hygiene as well as a bad attitude
I don't grin and bear it. I decline the appointment and tell them to leave just as some gentlemen will show up at a providers Incall and do the same thing. If I'm not having fun neither will you.

..... oh luv the only time i've had someone I just couldn't service it was because they were a dick (which is saying a lot because I can let even a little 'tude slide genuinely with a smile and i don't offend easy either).  It was 100% because of personality/actions not looks.  Too old or too big i've yet to meet.

Usually when the door opens I hear a shriek, or a fall to the ground crying "Oh god put me out of my misery", but that was just my ex-wife.

I always fear doing the opposite. I don't think I have ever showered so much in my life until I entered this scene. If I think that I won't see someone for more than an hour I shower again, using TWO different soaps. Worse is I always put on cologne, then forget I have no sense of smell so thus no clue to if I put too much on. Maybe I should just bring the cologne with and let the girl apply it

Yes this is an interesting thought. I do wonder at times if the other person finds my manly 6'5" 210 linebacker frame repulsive (OK I lied, more like....oh keyboard problems). Maybe more precisely others are as pathetic as I am in having really narrow tastes, or weird tastes. I know poor Natalia has had to suffer through all my weird stories (poor girl, someone needs to give her a hug) about my narrow minded tastes. So I do wonder sometimes if I am exact opposite of what they would find even as acceptable. But in the end you do the best you can do. Don't show up slobbering drunk, don't be rude, offensive, and insulting, and yes this may not be a "date" but there is no reason why one can't wear some nice clothes. Your not trying to impress her to fall in love with you, you are trying to impress her that you are worth her time to see again, or if need be go that extra mile we all need sometimes.

It really isn't about looks and that is an amazing skill I obtained upon providing.  You learn to like people for who they truly are and I suppose that will help tremendously in "real world dating" later in life.  After a while the old "your type" becomes a new "your type".  I am super attracted to an intelligent mind.
However, I have had some fellas that needed a shower.  When it's 115 F outside, it doesn't matter if you just showered....You can break a sweat from the car to the room.    So I just ask them to join me for a little shower foreplay=Nice way of saying wash your balls please.  I also refuse to see somebody that is drunk or crazy from drugs.  A few drinks-no problem.  Drunk-problem.  Just not my thing to deal with a crazy person that has altered behavior from a substance.

re: unattractive clients

I hate it when you guys talk about me

I don't have that problem. Being perfect ain't easy..

And I always get the BEST service available. Some providers even return the donation and take me out for dinner. Most of them agree that they should be paying me. Life is good.

I can find attractive qualities in almost everyone I see.  For some, I might find his sense of humor sexy...for the next, it might be his intelligence that turns me on...the next, I can get lost in his baby blue eyes and MELT!  Or maybe it is his commitment and love of his job/family.  All fine qualities!

I have only had to refuse two gents....both got a bit rough and hurt me.

I've never discriminated based on size, age, race, religion, or, LOL, because he was "homely"!  Smelly...there is a fix to that (soap and a shower) so even that is not a deal breaker, in and of itself.

Judging by what I see in the mirror every morning, I am guessing that most providers develop a high degree of tolerance for us ogres. A fresh shower and mouthwash helps tremendously. I think Ive had one encounter where she wanted to turn the lights off but I got a glimpse of her naked when we were done and I dont think it was for her benefit as much as mine, lol.