Negotiating with lenders

I have made an offer on condo and have been pre-approved by a lender. But I want to make sure I am getting the best interest rate so I reached out to 2 other lenders. Can someone level with me and tell me how much wiggle room lenders have for negotiation? For example if they quote me 4.375% interest, can I ask for 3.99% or is that just out of the question? What can I do to get the best rate and lowest monthly payment. Lenders, help me out here with some inside tips.