Some lenders offer an attractive interest rate to hook you in and later in the process it increases when it’s too late to go to another lender
There are also lenders who offer lower rates for the first 3-6 months of the loan but increase them after that. Often a higher rate at the beginning is better value for you.
What’s the reputation of the broker and the lender like? Some of the smaller lenders may not have the money to complete on the loan.
If your broker is not FCA regulated they won’t have direct access to all of the more established lower-priced lenders.
You can check the regulation by looking at the bottom of their emails or website and either they or the firm should be on the FCA Register.