Calculate effective PPI at the actual print size
The same file can be excellent at 5×7 and weak at 20×30. Evaluate the requested physical size rather than a generic image label.
Check clipping and tone for the output medium
Large clipped areas can lose detail, but bright backgrounds and artistic high-key scenes may be intentional. Use histograms as evidence, not an automatic pass/fail rule.
Make a small proof when the job matters
Paper surface, printer sharpening, ink, lab workflow, and display calibration all affect the final result. A small proof is often more valuable than squeezing another few pixels from software.