When I ask people to read for me, I expect them to be honest with how they feel about what they are reading. I may not like what they have to say, or agree with them but if they can't tell me they got bored reading a chapter, who will?
In return, I am honest with the people I read for. They have asked me to take time to read for them, and I assume they truly want to know my opinion. And I tell them what it is, always letting them know it is just that. My opinion.
So, how honest are you for your readers? Do you hold back because you're afraid you'll hurt their feelings, or do you put it all out there, hoping your words can help them be the best author they can be?