How do you know how rigorous a college (overall or in a specific subject / major) is?

[ucbalumnus]

@beebee3 @tamagotchi Here is a thread on the subject of small departments which may offer some courses infrequently:

Missing opportunity to take a course in a small department due to infrequent offering

Starting around post #84 of How do you know how rigorous a college (overall or in a specific subject / major) is? - #84 by beebee3 is mention of small departments offering some courses infrequently, so that a student expecting a course present in the catalog to be available may not actually have the opportunity to take it. How often is this an issue, either when considering colleges to attend, or being disappointed in the lack of opportunity to take such courses once enrolled in college?