A friend of mine shared this tip with me a few weeks ago, and it really, really works. When you get your berries home, prepare a mixture of one part vinegar (white or apple cider probably work best) and ten parts water. Dump the berries into the mixture and swirl around. Drain, rinse if you want (though the mixture is so diluted I find you can't taste the vinegar,) and pop in the fridge.
The vinegar kills any mold spores and other bacteria that might be on the surface of the fruit, and voila! Raspberries will last a week or more, and I've had strawberries go almost two weeks without getting moldy and soft. So go forth and stock up on those pricey little gems, knowing they'll stay fresh as long as it takes you to eat them.
Bon Appétit and Enjoy
YOUR Wonderful World!