Buying whole bean is already a minor refinement, you’ve ruled out anything that changes flavor as the grounds are exposed to oxygen. Buying whatever’s on sale also exposes you to a lot of variety, so you probably have much greater recognition of flavor differences regardless of preference. Not challenging your preference, only recognizing that it’s valid!

My taste in wine is similarly lax, but I set a price floor at ~$6-7 to avoid accidentally buying vinegar, and rarely go over ~$15-20 unless there’s a special occasion or specific reason to splurge. My only other criteria, which has never failed me: a pretty label.