There's a big difference in the way the two operate, what they can offer you and how they are paid. You should know the differences in their services when you are getting or renewing your mortgage.
A mortgage broker acts as an intermediary between the borrower and the bank or lender offering funds. A mortgage advisers job is to do the following.
Brokers in New Zealand must be licensed and registered with the Financial Markets Authority (FMA). They must also complete educational requirements to ensure the have the required product knowledge to advise members of the public.
Advisers are usually paid a percentage commission based on the amount of the home loan. This payment does not effect the interest rate you are charged.
A sales person at a bank has the same role as a broker with one exception. They do not "Hunt the market for the best mortgage option for you". A bank sales person can only offer the products available at their own bank. They seek value for you by knowing you personally and offering the suite of products available from their institution. For example, you may have your mortgage, a savings account, a credit card and even KiwiSaver all with the one bank.
The key here is to first understand that if you are borrowing for buy a home, you are the customer and you have bargaining power. There are often cash incentives for going with different banks and it's worth shopping around to see who has the best offer. There's no harm done in trying both. Any financial adviser should advise you up front how they earn their fees, if they don't, ask them at the beginning. Here's some key tips to help make a decision.