I am very thorough about doing anyone any favours, so I believe that makes me a desirable beta. One of my major cons is that my mood comes and goes and my muse often leaves me and my fans hanging for long periods of time, but I am a very responsible person and no matter how tough things in real life become, I'll squeeze in some time or make some if I'd made a commitment to someone's story, you can be sure of that. I have no idea what this "betareading style" is, but I can say that I try to be very concise when checking someone else's work.
As to expectations to anyone who wishes to acquire my services... Well, I guess what I can say is that I'd expect them to be serious in what they're writing about, not just wasting my time for their own amusement. I can't really think of anything right now which would make someone's work undesirable to beta but I'll probably fill this section out more as I come along or when I become more experienced.
I'll look forward to being of help to anyone who wishes it. ^^

I believe that I'm quite good at spell-checking and correcting any mistakes meaning-wise or phrases that are not concise. I'm usually a bit impatient when it comes to my own work but when it's someone else's story I'd check it twice or every three or more times before being content with the work I've done. I work hard to meet my own high expectations and I reckon that would be rather beneficial for anyone who chooses me as their beta.

Sometimes my eyes slip over the text and omit typing mistakes. Certainly not something incorrigible with a second or third read, but it happens often. I also may have an incompatibility with anyone who's thoughts and way of writing are too different than my own and my beliefs, thus making work coming along much more difficult.

I have only written romantic stories thus far so I think I have good reason to believe that I'd be better at editing those than others. I also like spiritual and philosophical writings over mysteries or such, for an example.
But overall there is not a type of story I wouldn't check just because of the genre.

I've never really fully got the hang of mysteries, horrors or thrillers so I might not excel much at dealing with those.