No idea where I read this short story, but probably 1975-85 and in an anthology.
There has been a murder in a cult community. The unique thing about this cult is that they don't believe in uniqueness.
To join them each applicant has to undergo extensive plastic surgery, and even bone shortening, to conform to a very strict set of vital statistics. Cult members are all of identical height, weight, apparent gender, hair and facial features.
I think they were referred to as "Barbies", after the doll, or something similar.
Since it's impossible to identify one member from another it appears to have been a perfect crime.
The protagonist is a female detective (private?) who despite being very attractive agrees to undergo the surgery so she can infiltrate the cult undetected.
Inside the community, she is able to solve the murder when she realises cult members can actually recognise individuals by something unique...
Afterwards she has surgery to restore her body.