In France, the legislation on credits being quite strict you are obliged to go through a recognized financial establishment (bank or specialist) which alone has the right to lend you money. In addition, approved intermediaries can help you (for a fee) and research the best proposals for your situation.
First, to get the most out of your loan, you are likely going to have to borrow from multiple establishments : it is extremely rare to find all the best deals with just one financing.
Second, you are going to have to negotiate the rates , especially if you are going to a bank that is not your current bank. Comparators can help you in this process but we strongly advise you to do a research yourself!
Sometimes they are able to actually lower their rates to keep (or acquire) you as a customer. Everything will actually depend on your profile (income, household composition, savings, mode of consumption, etc.). The best rates are offered only to the customer whom the bank thinks will be of good value to them.
These are financial institutions that only market home loans. Because of their specialization, they can often be more specialized on certain operations (credit in fine, rental investment ...) and give better advice. Some specialists are more expensive than banks. In return, they more often accept a little higher debt (if you are at 35 or 40% of debt).
These companies are specialized in the advice to individuals for the financing of real estate, or the repurchase of credit. The intermediary negotiates with credit institutions to obtain the best rate, to do all of the first steps. This service is not free and the offer made by the intermediary to his client includes his commission . It is then up to the customer to accept or refuse. In case of refusal the individual does not have to pay anything.