Hello kind people, I have no experience with plants and bought a few cacti and succulents from Home Depot. While potting them I noticed one set of cacti have brown spots. The flesh is dried over the spots and the prickles are falling off in that area. If I peel off the outer flesh it's dark brown but fairly dry and crumbly inside the crater (see images). Is this from over watering? Is there anything I can do to save them? I've removed them from the little plastic pot they came in and am letting they dry on a plate. Thanks in advance for any advice!
That looks like rot of some kind. Over watering makes it easier for pathogens to infect the cactus so should be avoided. Unfortunately, once deep inside it is difficult to treat and usually ends in the death of the cactus unless all infected portions are cut off. If these were my cacti I would cut them above the infection, let them dry a few days, then plant them in a mix that has excellent drainage. Here is a good article you may want to read on the topic: Black Spots on Cactus ... be sure to dispose of the infected portions so they don't keep spreading the pathogens.
