I want to shop for the best rate on mortgages, but I hear too many credit inquiries is bad. How many should I apply for?

I have a pre-approval letter from 1 lender on a loan right now, which I hear is good enough to use as a conversation-starter with home sellers. I don’t know if I want to go with this lender because there may be much better deals out there. However, each pre-approval is another hit on my credit record.

How many lenders should I let check my credit report before being worried about losing points?