"Opinion has caused more trouble on this little earth than plagues or earthquakes." ~Voltaire
It's always a good idea to have someone else read your writing before you deem it finished and send it out into the world. Because, let's face it, you're only one person with limited perspective. The more beta readers the better, because there are as many opinions as there are people. If you had 100 people read your book, reader 101 would point something out that everyone else overlooked. So would reader 102. But what if you don't like what some people are saying? And what do you do when some people love a certain part of your story while others hate it? Believe me, this happens all the time and, although it can be frustrating, leaves the writer where she should be: in charge of her own work.
How to handle advice
I always consider what my readers say. Even if it doesn't make much sense and my initial reaction to it is nausea. It's always a good idea to try to see where the reader is coming from. Possibly they reacted the way they did because your writing wasn't clear. Usually, though, when a reader suggests something I don't like, I end up tossing it in the end.
If more than one person comments on the same thing, I deeply consider changing it. If several people comment on it, there's something wrong with it and it has to go, unless, of course, they're giving it praise.
I've had a lot of stories critiqued by fellow writers and it never fails, there's always something that some readers loathe while others declare it their favorite part of the story. The main thing to remember is that it's your story. You choose what goes, what stays and how it all fits together.
Whose opinions count?
I most often have other writers critique my work. They know the craft, after all. And they're the most likely to take the time to give you feedback because they want some feedback of their own. But different writers have different styles and not everything a writer friend says about craft is going to apply. What they say as a reader, on the other hand, is the most helpful. Writers are definitely readers. Writers probably buy more books than anyone.
If you can get other people to read your unpublished manuscript, go for it. I don't care if it's your neighbor or the janitor at your child's school. Anyone who reads counts because they're the ones who buy books. They're the ones you want to please.