Pre-qualified vs. Pre-approved
The mortgage banker relies on you to provide an accurate estimate of your debt and credit score. Because your credit report isn’t directly accessed, there’s a risk of getting a less accurate estimate of how much you can afford.
A pre-approval is the most accurate option. It takes into account verbal information provided by you, in addition to looking into your credit report. This last part is key, since it allows your mortgage banker to assess your current debt-to-income ratio.
You can read more at this realtor.com article.