Here are six tips for How to Pick a Good Watermelon that's ripe and sweet.
Find the Field Spot - Look for a deep yellow color. If there's a white field spot, or no field spot at all, it likely won't be good.
Pick a Dull Looking Watermelon - A shiny appearance indicates an underripe melon.
Knock on It with Your Knuckles - Your knuckles should bounce off the melon, and the surface should be pretty hard/firm. Soft flesh indicates it's starting to spoil.
Get the Heaviest One for Its Size - This applies to pretty much all produce, but you want to pick the watermelon that is the heaviest one for its size. That means there's more water in it.
Check for a Uniform Shape - Some watermelons are round, some are oval, and either is fine. But if there are irregular bumps, this indicates the melon may have gotten inconsistent amounts of sun or water.
Look for the Sugar Spots and Pollination Points - If you see black spots on the melon, this is where sugar is seeping out and indicates a sweet melon. Also, if you see dots in a line (not a scratch), these are pollination points, and the more of them the better.