As a home inspector, seeing things like this bothers me, but doesn't shock me - because I see it far too often. How can you avoid hiring a contractor like this one?
First, do your research and read reviews. While not all reviews are accurate, they do at least give you an idea of what they do. Then, be sure to interview them and get to know them a little bit.
An important thing to keep in mind is not to base your decision based on price - you get what you pay for. Price is a factor, but it should never be THE factor. And finally, hire a qualified inspector such as myself to check the work over afterward to make sure they did a good job. Questions? Contact me