Begin with the actual reason
A denial or difficult preapproval can involve income, credit, assets, debts, occupancy, property, documentation, timing, or a lender-specific overlay. The first step is to identify what was reviewed, what was assumed, and what requirement was not met.
Look at the whole file
Complex tax returns, multiple businesses, changing income, business funds, rental property, condo eligibility, insurance, appraisal, and nonstandard property types can be missed or oversimplified.
A second look is not a promise that another answer exists. It is a careful review of available documentation and realistic alternatives.
Possible outcomes
The appropriate outcome may be another conventional lender, an FHA or VA structure, an alternative-documentation or portfolio program, a different property or transaction structure, corrected documentation, credit preparation, additional time, or confirmation that the original conclusion was reasonable.
The useful answer depends on the borrower, property, occupancy, documentation, lender or investor, and the rules in effect when the loan is reviewed.