Although there are several reasons for why your broker might have been able to get that low rate (eg his relationships with specific lenders, new lending programs, etc), the actual reason why is probably less of your concern. Just know that some lenders are willing to refinance at lower rates than they'd be willing to lend for new financing (which could be another reason why).
Besides, whether you're able to lock in 5.0% or 5.18% . . . both rates are considerably lower than 6%.... more