Proper ear-choosing etiquette (from our farmer friends) dictates that you shouldn’t peel back the husk to check the kernels.
In an ideal world, you would trust your source and know that the corn was picked at plump, sweet perfection, and you would know how to feel for plump kernels underneath the husk.
In the real world, lightning will not strike you if you choose to take a peek under the husk. But ask the vendor first.
Corn picked within a few days can be safely stored — in the refrigerator, please — for about five days before its sugars convert to starch.
Unless you’re going to eat the corn the same day, don’t be tempted to shuck the corn at the market; storing corn husk-on retains moisture and keeps the kernels plump.