It could be days before closing and something comes up but a good buyer's agent will have helped avoid this in the first place. The top 3 issues that cause closing problems are issues with the lender, appraiser and inspector.
Lender-a good buyers agent will contact the lender to first to make sure that the buyer is even approved. They will also let the buyer know up front what doucments the lender will be asking for. Most importantly a buyers agent will explain the importance of the buyer keeping their finances in check!! No more buying new furniture the day before closing!!!
Home Inspectors-some buyers don't understand that the seller has no obligation to fix anything that pops up on an inspection. A good buyers agent will do their best to negotiate on the buyers behalf to get as much done as possible.
Appraisal-its best to give your buyers a CMA for a property they are considering. In a muliple offer situation it may be tempting to go as high as possible but if the home doesn't appraise...then what??