I really don't know what to put for some of the topics here, so I'll wing it.
1. Who I am as a Beta reader.
I am a person who betas stories, I really fail to see how much more I can elaborate on that, I've been doing it for a while but it not like I'm famous or something ^^
2. My Beta reading style.
Logical mostly, I tend to over-elaborate, especially when I am really enthusiastic about the story, try not to criticize but guide in the right direction, especially since I know that many people write with English as a second (at least) language.
I expect the author(s) requesting my services to respect my opinions and the time I take to comment on various flaws, inconsistencies or errors in the stories I beta as I try to be as meticulous as possible, which is mentally taxing and time consuming. I expect the the author to be willing to have disagreements and relevant discourse if they hold opinions or views that differ from mine, except for grammar and typographical errors, I mean come on, how can you dispute something like that, it has rules dammit! (and yes I do take slang or improper spelling for characterization or clever/toilet humour into account)
Obviously someone cannot beta what they don't know, unless only asked to beta the language mechanics (which I can easily do).