I tested Nettie the other night, and my first few attempts failed, but after multiple attempts - which I was doing to check the DC of all the checks - I did get successes as well. The real problems with Nettie are:
1) It's three DC 10 rolls, where you need 3 successes and 0 failures, which is the equivalent of a single roll of DC 17.
2) Your only options are Charisma-based - Intimidation, Deception, Persuasion, so they're all going to be pretty much the same difficulty.
Either it should be one roll of DC 17, or else it should be a skill check, where you need X successes before Y failures (where X is greater than or equal to Y, and Y is greater than 1), or else the first few attempts all continue the conversation, but your success or failure affect the DC or advantage/disadvantage of the actual check.
I *just* started doing this, but im halfway through this playthrough. Next one I plan on making a better system.
I'm pretty sure that at level 4 a DC 30 check is going to be an auto-fail even rolling a Natural 20. ... Yeah, you got a 25 with a +5 modifier. I guess you're just rolling the dice to check the rolls generated?