Unlike some trickier fruits, berries are relatively easy to judge for ripeness. Their colour is a good indicator, but, as the Kitchn points out, there are some subtle signs that berries are about to spoil.
Photo by liz west.
Oddly enough, the container can be an indicator of a berry gone bad. They explain:
The container they're in is wet or stained.
That's probably a sign of overripe, mushy berries in the bottom of the basket. Since you can't dig through the basket to find out, checking the bottom and sides of the container is a good indicator. Typically there's a mouldy berry in a container sporting these signs. Your best bet is to pick up a new carton.
Of course, this won't always be the case, but it may be a sign to at least double check the berries you're dealing with. For more detail, head to The Kitchn's full post at the link below.
5 Telltale Signs You Shouldn't Buy Those Berries [The Kitchn]