Your rate depends on many factors. Your credit score, down payment, the type of property (i.e. single-family detached phone vs a condo, etc.), second liens, and the transaction type are just some of the factors that weigh in. It is for this reason it is so important to meet with your mortgage broker a couple of months prior to shopping for, or, planning to purchase a home. There are ways to get prepared should your credit score be lower, or your assets are not in place. A good mortgage broker will make recommendations on how to handle your credit issues so you can obtain a better rate. 

Also, unlike a retail bank, a mortgage broker can shop your rate with many different lenders, thereby facilitating access to the most competitive rates in the industry. There are many lenders that do not have a retail presence, therefore can offer borrowers more favorable rates. Leveraging the assistance of a mortgage broker gives you access to greater choices, and therefore, better rates and terms.  There are also many different scenarios that a broker is equipped to handle, i.e. self-employed individuals, people with lower credit scores, investment properties, etc.