keeping blackberries fresh

I love fresh berries, but I got tired to having to toss them because they went moldy so soon after buying them. Someone suggested that I place them (unwashed) in a large flat dish that would hold them all without any of them touching - then covering the whole dish with foil so they are "sealed". I will never just leave them in their container and stick them in the fridge. They stay amazingly fresh and I get to eat every last one of them. BTW, I wash them just before eating. We also do this with strawberries. Haven't tried them with raspberries yet. Usually eat them all when purchased.