The thing is, almost everything I write either has lesbians or something else I better not mention here in it.. And it came into my head one day to wonder if women even like lesbians in their books.
Looking at different aspects of the question:
Q: 'Can f/f sell as Romance or Women's Fiction?'
A: Probably not.
We're talking about
marketing categories here.
(That is,
where do the books go on a bookstore shelf.)
Going by what I see on the shelves, f/f love stories are not going to be marketed as Romance or as straightforward 'woman's fiction'.
Q: 'Can f/f sell as erotica?'
A: Yes.
We got erotica folks here who can give you a better take on the erotica market. But I've seen excellent print collections of f/f erotica, so f/f is out there.
Search erotica / Lesbian at Amazon and see who's publishing them.
Q: Can f/f sell in other genres?
A: Without doubt.
Marketing Categories like Mystery, Horror, S.F. General Fiction, Literary Fiction sometimes have Lesbian protagonists.
In these case, the core of the book is not the love story but the mystery, horror plot, alien society, etc. An f/f love story can be a major part of the book, however.
Q: Do women like to read stories about Lesbians? Do men?
A: *shrug*
In spite of all the glossy covers on the magazines at the check-out line, it is impossible to make meaningful generalizations about, 'what men like' or 'what women like'.
Talking market -- a writer doesn't need universal popular appeal. She just needs a readership.
Q: What about selling 'something else I better not mention here'?
A: Wildly guessing here at what you might be talking about-- and assuming it's not political or something -- then I'd say -- limited.
Specialized kinks like water sports, SM, incest, and beastiality are going to be a small part of the erotica market. If you write it, you probably already know where it sells.
No. You can't sell them as genre Romance of Women's Fiction.