Not all mortgage advisers work across the whole market, many estate agency brokers only source mortgages from a limited panel of lenders.
One way to do this would be to seek the advice of a specialist, who will be able to guide you through the mortgages on offer and find the correct one for your circumstances .
Also, by providing all of your financial information to a broker based within the estate agency selling the house, could cause a conflict of interest and reduce your bargaining power.
Getting impartial advice when taking out a mortgage is always a better option, and choose a broker working just for you.