Your buyer does not have a Pre-Qualification; he or she has a Conditional Loan Approval.
Every Loan Approval starts out with a list of conditions. Even for a perfect borrower, conditions such as an acceptable appraisal, clear title, title insurance, verification of funds to close will be listed on the Commitment Letter. These items must be "cleared" by supplying the appropriate documentation to the underwriter, and the underwriter must approve the documentation. Once all of the conditions are "cleared" the underwriter signs off on the Approval and the loan moves to the lender's closing department to prepare the loan package.
This is the standard practice in the industry to fund a mortgage. A buyer doesn't have to "agree" or "disagree" to the conditions in the same way he or she would agree or disagree to conditions in a purchase agreement. It is mandatory that they be cleared before the lender will send the loan package and funding to closing.
I've seen Commitment Letters with 40+ conditions... and I've seen them with just 4. But if your borrower has a Commitment Letter, you are close to finalizing your sale.