Buy quality whole beans from a reliable purveyor (preferably a roaster). If you don't have a grinder at home, ask a salesperson to grind whole beans for you rather than settling for pre-ground. Purchasing bulk (unpackaged) beans from a specialty shop is okay as long as the bins or jars are relatively small and refilled regularly. Large vats hold a lot of beans and therefore don't need frequent filling. That means that beans can hang around for a long time being exposed to light and air. That can mean stale beans, and staleness is not a desirable attribute.