I'm new to TER, been looking for providers and reading many juicy reviews. My concern is, does race/size matter for the providers to have good chemistry with you?

Racial discrimination DOES exist in this game. You'll find a few ladies who have a "No AA" policy. It's sad but true.  As for size, I've never seen any girl who asks in advance how big your wang is. But I also hope you're aware that not all AA men have big dicks and not all of us white boys have dinky wangs. I've had at least one great gal tell me she could no long see me because my cock made her too sore.

You don't say whether you are a person of color or if you are amply endowed ... or if you are just asking for a friend or out of curiosity.  
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When these threads on these topics come up, one suggestion is to disclose relevant info in your polite intro email. You don't want to show up her door, have her look through the peep hole, and say, "Sorry, no AA." Your email might say, "I am a 45 yo AA gentlemen who will be visiting NY in December on business. ..." There are also suggested ways to introduce the size issue but maybe not in the first email.  
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Even if someone doesn't explicitly say "No AA" in their ad it's best to know ahead of time if it's an issue. Another consensus point is that it isn't worth fighting over a "no AA" reply. A grudging willingness to go through with a meeting could just be a big disappointing session. Just move on to another Provider for whom it isn't an issue.
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Good luck! Have fun!

I see admirers of all ethnicities. I love getting to know men of different backgrounds and I've never asked ahead of time for their ethnicity.  

A little about me: I'm a 27 year old French Latina based in New York. I'm an all natural 36DD submissive little princess who loves to please and I offer GFE.  Take a look at my site and let me know if you're interested

I'm a multi-racial dude with AA ancestry (1/4).  In my experience, and I usually see Asian gals,  it is rarely a negative issue, and has actually been at times a "plus" --- "Oh, you look a little like Obama??  Sexy..."  I never respond to ads that specifically say, "no AA" but from time-to-time, if not mentioned in the ad or on the site, it may come up during the appointment call.  When I have spoken with some provider/friends about this issue, it is usually a concern with the gal in question buying into a concern or fear of criminal/fraudulent behavior.  For example, one provider friend told me that a heavyset AA dude came in and faked a slip-and-fall accident.  I've seen ads more than a few AA FEMALES providers who will explicitly state "no Black men" or "no Black men under 40."

As to size, as someone commented, not all AA dudes are Lex Steele.  But that said, I am admittedly on the large organ side and I have had only one provider tell me (after giving me the table shower) that she couldn't service me because I would be "uncomfortably big."  I've had a handful of others who have expressed initial concern and asked me to "start slow" and it was fine.  And of course, I've had some gals who look at me being plus-sized before the session and were eager for my  plus size.  Some women really do enjoy big cocks.  

Like anything, it ultimately depends on an individual's preferences, life experiences and the impact of societal stereotypes.  Latino men will also face some discrimination due to stereotypical criminal/scam concerns.  And other ethnicities will face issues of concerns based solely on negative stereotypes as well...I knew an indie who refused to see Orthodox Jews and South Asian men based on a "they smell" stereotype.  It's wrong and unfair but there's no reason to think that this business sector is any more enlightened than the society as a whole.