I am suggesting that a new sub-category be added to the search criteria regarding breasts, that being “nipple appearance”. Some descriptions could be “stiff”, “soft”, “inverted”, etc.

I love to play with and suck on erect nipples, but not all women achieve them, even after being aroused.

Some providers mention their nipples in their ad copy, (e.g. the recent NYC Buzz by Suzanne Stevens) but it would be helpful if clients provide this bit of information after seeing a provider and posting a review.

I have to disagree with this suggestion. I can't see guys adding such info to Profiles in the first place. Neither do I see it being added accurately or uniformly.  Although you suggested "stiff" "soft" "inverted" etc. there are probably much better terms used by professionals (professional plastic surgeons, not Professional mongers!). Some areola are big / small; smooth / bumpy; etc.. What about Piercings? Or "sculpted"(?) - I heart shaped nipples (via surgery: nipple shaping or nipple grafting).
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I think a BETTER suggestion would be TER would make the Details sections searchable.  I think that it would be cheap and easy to scan all the reviews (well, start with 2025 and only go back 5 years(?) or so) and create a flat text index file. Searching flat text is fast, CPU-cheap, and easy. Search "pencil erasers" see what pops up!  
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Improving Review searching would address MANY similar suggestions.