With just a few tips and facts about how to tell a ripe cheese from one that's not, you'll be better equipped to pick out the perfect piece-- all by yourself.
The most important fact to keep in mind is that cheese ripens from the outside in. Unless it's a blue cheese, which is the only style that begins ripening from the inside, ripening action is initiated by molds or bacteria on the exterior rind, which then begin the process of breaking down the fats and proteins on the interior of the cheese.
The following guidelines refer to softer cheeses like bloomies and washed rinds. It's for the way in which they age that these two styles of cheese are called "soft-ripened" cheeses, since they become softer and softer over time.
This is fine-- and can be preferred, actually. Variation in flavor and texture is often something that will enhance your experience of a cheese. Getting a slice of cheese that has distinct texture in rind, creamline, and inner paste is almost like having three cheeses in one. And the contrast between the mild middle and the more developed area beneath the rind is quite pleasant.
The aging process will continue until a cheese is eaten. The chaulky, dry interior of that slice of Humboldt Fog, for example, would become as creamy and assertive as the creamline, if left to ripen on its own. But the trick to a perfectly ripe cheese is getting a balanced proportion of ripeness. If we were to allow this cheese to ripen all the way through to the middle, the interior would be oozy and ripe, but the portion closer to the rind would become overripe: stingingly assertive, out of balance, and ammoniated. No good.
One of the best ways to ensure that you have an evenness in ripeness is to touch your cheese. It's especially easy to do this if cheeses happen to be pre-cut in the case. A cheese shouldn't be too soft, and the rind should be fully entact-- no oozing of the insides from cracks in the rind. A washed rind or bloomy rinded cheese shouldn't be too much softer than a very ripe banana: soft is okay, but it should still have some give. You can also examine your cheeses visually. If the cheeses are wrapped in plastic, you'll be able to ensure that the creamline hasn't made its way to the center.
Ripening happens much more slowly in the case of harder cheeses like goudas, cheddars, and mountain cheeses, like the one below:
But even here you can tell that the area directly beneath the rind is more aged than the center. In this case, with harder, aged cheeses, this area will be drier, darker, and harder, becoming, in a way, more like the rind. With hard, super-aged cheeses-- Parmigiano Reggiano is an especially good example of this-- the portion of the cheese closest to the rind can often have less flavor because it's lost so much moisture and become so hard.
As always, make friends with your cheesemongers! Ask what cheeses are perfectly ripe. Remember: Cheeses are living and breathing in their own special way, and so their level of ripeness is ever-changing.