Though I speak with the tongues of men and of angels, and have not charity, I am become as sounding brass, or a tinkling cymbal. And though I have the gift of prophecy, and understand all mysteries and all knowledge, and though I have all faith, so that I could remove mountains, but have not love, I am nothing.These aren't universal, unqualified rules and I don't understand why you're trying to generalize them beyond fundraising. To use a different and perhaps silly example, I'd be more inclined to trust my intuition with respect to dog kennels than, say, medical or legal advice.
I think pg is saying that fundraising is more like medical or legal advice and less like dog kennels. He's not making a blanket statement about trusting people with prior experience.
If you want to make this more mathy, imagine there some function
I(s) = amount I should trust my intuition in situation s
pg is writing about what happens when "s_1 = I'm fundraising for the first time," but you're trying to rebut his point as if he were writing about what happens when "s_2 = I'm talking to someone more experienced than myself." There are three possibilities: pg believes I(s_1) = I(s_2), you're misunderstanding pg, or pg is contradicting himself.
You're arguing that since pg believes I(s_1) != I(s_2) (as evidenced by his previous writings) then pg must be contradicting himself. The correct line of reasoning is actually "If pg believes I(s_1) != I(s_2) then either pg is contradicting himself or I'm misunderstanding pg."
Given pg's generally fastidious nature with respect to these things, I'd say the prior odds of pg contradicting himself are much lower than you simply misunderstanding him. At the very least this is what most folks believe, so when you jump to the conclusion that pg is contradicting himself you come off as an uncharitable little troll. First stop on the troll tour: Downvote City. :D
Putting on my teacher hat for a second, when you smell a contradiction like that it's often a sign you're misunderstanding something. Rather than point out the apparent contradiction and go all j'accuse on the author, it's more useful to stop and ask yourself, "Assuming the author is intelligent enough to spot a contradiction like this, is there a way to understand what they wrote in a way that isn't contradictory?"
There's really no downside to doing this, even if there is a contradiction. At the very least you'll have developed a more robust argument. Often you'll end up with a way to express the author's argument more clearly than the author did in the first place, since you're probably not the only one confused in the same way. What's more, if there actually is a contradiction, folks will be more inclined to believe you when you demonstrate you've gone out of your way to try to understand the author.