Depending on where it is, it's pretty easy to examine it yourself. On my 2004 WRX the A/C and accessory belts are right there at the front of the engine where I can place my finger there to check. My A/C belt was squealing, so popped the hood and felt it. The rubber was noticeably brittle with lots of little chunks missing. I can't exactly describe it, but anyone who has experienced a worn belt knows what it's like. I don't know how to do it myself, but paid someone to do it. He charged me $85 to both replace my cracked radiator (provided by myself) and install two OEM belts. He actually did it again later - not sure what happened but the belt broke. I also needed a timing belt replacement at that time.
I had a serpentine accessory belt fail on my wife's 2002 Civic LX. Never really thought about it until it went bam on the freeway. I could see a small piece of it that fell to the ground and I then smelled burning rubber. When I got off the freeway I parked in the first place I could and saw that it was still being driven on a single rib. So I limped it to our destination until I figure the entire belt broke off, and all of sudden the radio went out and then finally we lost all power. I had to awkwardly park it where it was partially blocking a driveway. The residents later came out and were understanding when I told them that my belt was gone and it had no power to do anything. I figure after the belt eventually gave out the battery took over as long as it could. I had it towed to a local shop that charged me maybe $125 to replace that and the A/C belt, but I did get a $25 gift card. However, I could see what remained of the old belt, and it was severely cracked/pitted.
At least on that car the timing belt (which I know is on borrowed time) drives the water pump, so at least there was coolant flowing.
Here's a primer on the various ways that serpentine belts show wear/aging/damage:
https://fifthgear.biz/fifthgear-blog/how-to-tell-when-you-need-a-new-serpentine-belt/
I've seen cracking, but where the cracks were literally little V chunks where pieces of the rubber had come out. You also need to know the kind of serpentine belt. The Gates/Mitsuboshi/Bando belts on our Japanese makes use smooth ribs, but some belts have textured ribs, so you can't necessarily tell by just feeling it. You'll have to see if it's cracked or just feels like there are cracks. This one looks different than any belt on my cars, but I understand it's normal and in good condition.