Ever chosen fruit at the grocery store that looks fine, only to get it home and realize that it's dry, colorless and flavorless on the inside? Grapefruit is known for its juiciness, yet sometimes after slicing it open, you find that inside it's not what you expected.
Scan the grapefruit display for a fruit with a bright, even color. The shape should be fairly symmetrical.
Hold the grapefruit in your hand. Lift it a few times. It should feel heavier than it looks. This indicates juice on the inside.
Avoid grapefruit with soft spots.