First, you should be aware that mortgage loan officers are primarily salespeople (including your humble question-answerer). An essential part of selling is getting the other person to commit to moving forward. From the salesperson’s standpoint, consent to run a credit report is the first step in that process.
Many loan officers will tell callers shopping for rates that they can’t provide an accurate rate quote without having a credit report. That’s not entirely true, but the rate a borrower can get is a function of their loan-to-value ratio and credit score.
Fannie Mae and Freddie Mac, the investors who buy most residential mortgages in the U.S. and whose guidelines lenders follow, use risk-based pricing to determine adjustments to the “raw” (unadjusted) rates for the day. All lenders who sell to Fannie and Freddie are subject to the same adjustments.
A borrower with a 740 or higher FICO score will get the best rate. A borrower with a score of 730–739 will get a rate roughly 1/16% higher. With a score of 720–729, their rate will be about .25% higher.
A credit score is not the only factor determining a borrower’s rate. The type of property (single-family, condominium, multi-unit, etc.) also plays a part. So does the use of the property—owner-occupied or investment. A loan for more than $548,250 will also carry a slightly higher rate.
When a lender publishes their rates, they assume the best possible scenario: 740+ FICO score, 40% down, single-family owner-occupied.
You can get a rate quote from a lender by asking in the right way—including the variables that affect the rate. Here is how you could ask your question.
“I am planning to buy a detached home with 20% down. I am looking for a 30-year fixed-rate loan. My FICO score is over 740. What rate could you offer me with no points if I locked today for 30 days?”
When they give you a rate, ask what their fees for underwriting and processing are. The other closing costs—title, escrow, appraisal, etc.—are third-party fees and will be the same regardless of the lender.
If the loan officer tells you they can’t give you a rate without running your credit, go to a different lender. They are playing games with you.
Keep in mind also that rates change every day. A quote that you received a week ago is worth nothing today.
Finally, in keeping with the helpful spirit expressed in a previous answer (TL;DR):