When comparing quotes prior to getting works done it's important to compare not only the scope of works and price but also the Terms and Conditions that comes with the quote.
Often people will bypass reading the Terms and Conditions when choosing a quote but reading it is vital as one of the things it will tell you is the warrantees given.
This can make a difference when it comes to paying once for a job or paying more than once when the results are short-lived and the work needs to be done again. For example, some companies may only offer guarantees on work for up to a year while others may offer no guarantee at all.
So before choosing a contractor make sure you have your bases covered otherwise you could end up spending a lot more money on a contractor that initially you thought was going to be the cheapest.