The main reason that authors use beta readers is to get honest feedback about their book, which they can then use to determine if improvements can be made ahead of publication. While we do expect our beta readers to be respectful in their answers, they would be of very little use if they were afraid to provide negative feedback to questions you’ve asked.  So if a reader has an issue with something in your story that you’ve asked about, you should expect (and hopefully want) to hear about it.

Given that, authors that use beta readers should have a thick skin and be able to hear criticism about their work, although they are never under any obligation to act on any of it. 

Everyone comes from different backgrounds and have their own personal biases, and this sometimes colors how we see the world or react to certain things.  Thus any feedback you get on your book, whether it be from a random stranger, on a review, or even through a beta read, should keep this in mind. Some types of questions have the potential to be more affected by this sort of thing than others, which is why an author needs to carefully think about all the feedback they get before deciding on whether it warrants making changes to their story. 

This is why we have a minimum order of 2 beta readers per order, and definitely suggest more when possible. With only a single opinion it is much harder to determine if any possible personal bias or preference came into play in an answer.  But with multiple responses to the same question, you can look for common issues or complaints.  If more than one person has the same sort of issue with a character or aspect of your book, this is a good indication that you need to examine that problem closely.