Oil change shop says alternator belt is cracked

[RMcG]

A local oil & filter change shop told me I needed a new alternator belt, because the current one is cracked. They told me this when the car had 90,000 miles on it, it now has 91,000 miles on it. It is a 2008 Yaris, base model hatchback. It would have cost quite a bit to have them replace the belt, $80-$100.

The belt is a serpentine belt. I looked at it and felt it with my hand as much as I could and I cannot really say it is cracked or worn, but I am not an expert at all.

QUESTIONS: Is it likely the belt is worn enough to need replacing? Can I assess the wear of the belt myself?

Am I taking a great risk if I do not replace the belt right away? How hard would it be for me to replace the belt myself?

Thanks,

RM