yeah, everything in this game has no guarantee.
1) you have high on smart, but not necessarily managed to analyze all PE in crime scene.
2) you have high on charm and JOC tells you that the suspect will answer better to charm and you've used charm, but the suspect clammed up.
3) you have high on smart, you've used surveillance, but it doesn't always work.
there's 4 PE townies and at least 6 - 7 WE townies in each cities and you're only able to get one of each if you're lucky and have at least 80% of not able to solve all cases when you didn't get the cases that depends on your PE contact, so what's the point of getting high xp, go for AVH, earn gold equipments, yet everything comes down to "doesn't always work".
if 30 in charm guarantee 3 more answers from suspect upon questioning, 20 for 2 and 10 for 1, then it would be better for players to know when to ask for answer.