Some personal red flags that make me hesitant to betaread
"it's [list of tropes]" and nothing else, not a fanfiction
At least put minimal effort and write a proper blurb. Bad blurb is still better than list of tropes. I get it when it's fanfiction, since I'm already familiar with world, characters, etc. I don't get it when world, characters are unfamiliar to me. I know it's hard pill to swallow for some, but liking fanfiction is not about tropes, tropes and just tropes. Pitch me your story and not fanfiction version of it.
"I know you don't like x but I want you to read my x"
I strongly believe that having an outsider of genre/trope give feedback is beneficial to the work. Is the love interest "morally grey" or just violent and abusive? Is magic society a society or is it weirdly "sexist but justified"? Is an explanation for interstellar travel possible to graps, or is it so intimidating that reader not into technicalities feels compelled to skip it?
That being said, about three of four people who hit me with this are not interested in this. They want to write "x so good that person who doesn't like x will like it". And it's... very adamant.
There is big difference between "need someone who isn't into genre conventions to check if it doesn't come off too weird" and "did you like? ok but did you like it? you told me that it came off as a/b/c so you didn't like it?". Which lead us to:
"I think you will like it"
I'm absolutely not picking up any book for feedback if this is how it's pitched to me with no previous experience with each other. Been burned before and I do not know what I'm supposed to do with such an expectation and what the expectation is.
a) just a flavor text at end: neat. If it's ending of bigger blurb/summary it's usually well written too.
b) consciously using as "set expectations high I'm feeling confident about this" after few rounds of feedback/betareading: good stuff. Glad we both are enjoying our time.
c) it caters to my specific tastes personally and I indeed like it: nice surprise to be sure, but who is target audience. It's can't be only me.
d) it tries to cater to my specific tastes and I don't like/I hate it: is this what do you think of me. Is this what I am in your eyes. I feel like I should feel offended.
e) it's "you don't like x but you will like my x": N̷͕̹̱͔̯̯̘̭͉̲̩̐̏̎̃̉̓̀̓̈́̒͑̀ͅÒ̸̧̭̜̟̜̾̾̽͒̓̚.̵̩͔͎͍̻͎̝͇̻̜̬̜͂͐̆̈́̓͘̕͜ͅ don't know how well or unwell screenreaders deal with zalgo: it says "NO." in caps with angry period.
f) it doesn't try to cater to any of my tastes and I don't like it: this is straight road to getting accused of hating it out of spite. I must be trying hard to not like it. How could I not like it. Why I'm getting asked about liking it again when firstly I was asked to do the usual feedback.
"it's [title/trope] but subverted"
Please don't start with this. Let your writing be itself first. Are you sure it's "antisomething" first and not your own story? Because I will read it as anti-x/subversion of y first and plenty of works that are mainly anti something or subversions fall flat, fall back into tropes or don't have anything interesting to say. Is it satire? Comedy? Spite fic? Love letter? Are you sure it's the right tag line?
It's a rather common pitfall of this premise, but I don't want to take part in it if subversion is the only substance.
"I heard you are harsh and I can take harsh critique"
First of all I'm blunt. Will not force myself to either sugarcoat it or to tear it down. Second of all; people's passion for enduring "harsh critique" is greater than their passion for writing, and I'm there to do writing things. That's assuming they are not lying or overestimating their tolerance for having writing examined.
...Oooooor wants pat on the back and bragging right how they survived harsh critique.
Used to think it's reassurance but guess what. Of course, not all people use phrases in same way and same intentions.
will not answer questions or gives evasive answers
I'd prefer to know what I will be working with. And that I won't get unsolicited porn again.