Closing concessions? What is your strategy?

[Alex Yost]

After flipping a few homes, we have found that buyers can be pretty aggressive in their requests for "repairs" during the due diligence process.  Unless we note otherwise in the listing information or disclosures, we fix everything that is broken or not functioning properly, but we have had several recent requests that are expensive and I'm interested in your experience in handling things like:
- this roof is old and we're worried that we may have to replace it (was inspected by roofer and determined to be functioning properly)
- there are screens missing from some of the windows and we would like you to add them
- we're concerned about the drainage and would like you to add gutters
- the AC unit is old (age disclosed in disclosure docs, was tested by HVAC guy and running fine)

 So do you budget for this type of concession, do you "meet in the middle" or do something else?  Typically the houses we rehab are 20 - 50 years old.