Your monthly payment and interest rate will never go up. Often with no closing costs. Mortgage brokers are different from a direct lender. Brokers can not approve or fund your loan. Instead they become middlemen usually selling your loan to a direct lender who pays them the most for it.
Many lenders have cancellation charges as high as several thousand dollars.
Insist on no cancellation fees before you apply. Real Estate companies often have financial relationships with mortgage companies to make extra money. The better your credit, the better rate you should get because your loan is not as risky as others. The shorter term the lender has to fix the rate, the lower the rate will be. This is because the lender is able to push future interest rate risk on to you.