What Paul said. And, I think, the crucial thing is to come to an understanding between author and beta on what the rules are and what each expects of the other right at the start, before you even open a story file. That way there are no unpleasant surprises.
If you know in advance that Author A is only wanting praise from you or just wants you to read through the story and give them an overall view of characterisation and plot, then you know not to waste your time pointing out those typos or glitches.
Equally, if Author B says, "Give me the works, anything goes and don't hold anything back..." you know they won't freak out when you do just that. (Or if they do, you can always remind them you're just doing what they told you to.)
As Martha says: Communication is key!
LabRat
