At beauty school, James Kivior learned how to shape eyebrows, treat dry skin, and reduce under-eye puffiness. What he didn’t learn, he said, is tact.

“When I started, I didn’t quite know how to speak with clients,” Mr. Kivior, an esthetician at Paul Labrecque Salon & Spa on the Upper East and Upper West sides, said. “Proper etiquette is not something that they taught us in school.”

With a decade of experience under his belt, Mr. Kivior now knows what to say — and what not to say — to the women and men who come to him for hair removal or skin treatments. “You don’t want to insult them in any way,” he said. “I’ll say, ‘I see you have some activity on your face,’ rather than, ‘Oh my God, you have a face full of pimples.’ If someone has a lot of blackheads, I’ll say, ‘You’re congested, and we’re going to work on that for you today.'”

Not all beauty professionals are as diplomatic as Mr. Kivior. Many well-maintained New Yorkers grumble that they often leave salons and day spas with their egos bruised after an esthetician or stylist pointed out their rogue hair growth, large pores, or thin mane. They say persnickety technicians — all too happy to comment on their clients’ dirty fingernails, to point out how much hair had to be removed from one sensitive area or another, or to badmouth a former colorist — can sour what was supposed to have been a calm day at the spa.

“I go to relax,” an editorial assistant at a fashion magazine, Brette Polin, said. “I don’t need the comments.”

Ms. Polin said she was dumbstruck recently when the woman waxing her unwanted hair offered up a backhanded compliment. “She said, ‘You’re so beautiful, and you’re so hairy,'” Ms. Polin recalled. “I felt like saying, ‘Thank you for the first comment, but what was the second comment about?’

You’re there because you know you have a problem. They don’t need to tell you about it.”

She attributes the hurtful running commentary to an esthetician’s lack of sensitivity, and their desire to sell clients products or additional services. Ms. Polin, who lives in Murray Hill, said she’s less likely to make a purchase after being offended. Though she’s never snapped at beauty professionals who she felt have “crossed the line,” she has wondered whether they’re in any position to judge. “You’ve got people saying, ‘You need to do this, and you need to do that,’ and sometimes they don’t even look so great.”

There’s no gentle way to approach people about their flaws, writer and director Nora Ephron said. “When I make the mistake of wandering over to the cosmetics counter, I notice that I’m sometimes told, ‘Your skin looks dry.’ That’s the sort of comment I can live with,” Ms. Ephron, who discusses the perils of her beauty regimen in her new book of essays, “I Feel Bad About My Neck: And Other Thoughts on Being a Woman” (Knopf), said.

Ms. Ephron, 65, estimates she spends about eight hours a week on her hair, skin, and nails. She said she finds it most unsettling when someone points out the hair on her upper lip. “The woman who threads my — I’m sorry to say — mustache is constantly telling me I need to have it done way before I ever think I do,” she told The New York Sun. “It makes me think that either I have been running around town for days looking like Adolphe Menjou, or else she is lying to me. But you know what? I let her do it.”

To one Upper West Side resident, Brooke Moldenhauer, what is said matters less than how it is said. She said she hadn’t realized that her eyebrows were not quite symmetrical until a beautician pointed it out to here recently. “She basically just asked me who I had gone to before, and said that I needed some work,” Ms. Moldenhauer, who is 25 and works in the financial services industry, said. “But she was really nice about it, and did not do anything to gross me out like show me the hairs she plucked — yuck.”

Pointing out imperfections can sometimes be a turn off — not a catalyst — when selling clients on treatments or procedures, Gustavo Souto, who consults with would-be patrons at Quick Bleach dental spa in Midtown, said. “When a patient comes in, they’ve already noticed that their teeth are a less-than-ideal color,” he said.

To avoid making clients uncomfortable, new hires at Le Petit Spa on East 48th Street go through sensitivity training, the manager, D.J. Pesta, said. Ms. Pesta said that while no conversation topic is inherently off limits, she teaches spa staff to take the lead from their patrons. “We don’t ask women why they’re letting their mustache grow,” she said. “We ask them what they like to have done. If they don’t see an issue, we don’t see it for them.”

The spa’s estheticians are encouraged to ask clients about what prompted them to make an appointment, rather lunge into the types of treatments they “need,” Ms. Pesta said. “It’s all about how you say things,” she said. “We don’t want them thinking, ‘Oh my gosh. What did I look like when I came in here?'”