Top Twelve Signs Your Lesbian Erotica Was Written by a Dude:
1. The first piece of information you learn about the object of affection is her boob size, generally in direct comparison to the heroine's. Both are still at least a cup size that's a failing letter grade.
2. Rather than explain to you why such an attractive lesbian is single, he explains why such an attractive woman is gay. Also, she must indicate by word or deed a continuing interest in at least occasional straight sex and why that's of such great importance to her.
3. Not content to allude to M(+)/F(+) as needed by the storyline, he writes full straight sex scenes. If and when confronted in comments, he will argue that there's more gay sex in the story than straight or that graphic and frequently brutal/rapine sex is a key contrasting point to what he can only imagine lesbian sex to be. You are as convinced as you would be by a chef who tells you that there's more chocolate than tuna in the brownies he made or that canned and mostly rotted tuna is a key contrasting point to the chocolate.
4. Characters can be tomboys, punkish, athletic, or dominating, but they cannot be in any way masculine. Their dialogue, however, all sounds as though they woke up female for the first time that very day, causing them to become surprised by and consequentially have to reason through any and all seemingly unfamiliar emotional or physical reactions to common stimuli.
5. At some point, a woman's clitoris is "sucked like a miniature cock."
6. The entire story actually makes much more sense if you replace "boobs" and "nipples" with balls, "clit" with dick, "pussy" with asshole, and "g-spot" with prostate, then read it as gay male porn. (This is frequently coupled with a very tenuous grasp of female anatomy on the part of the author in general, so he'll occasionally add clitoral/anal sex or something similar that makes no physical sense if the characters involved are human women.)