They had to be rich.
The ostensible purpose of the system was to protect the privileges of old money, but no government ever wants to do that. The true purpose was to enfranchise the new money.
So the heralds were like most consultant genealogists until modern times, and some still - they were mostly in the repairs and improvements business, with the occasional new build.
But they're hard to pin down. Nobody can do a complete analysis of their "records" because they aren't public. You can see a copy of a Visitation pedigree and see where it's been tweaked and why, but you can't prove who did it. You can see a bogus parchment scroll with a herald's signature on it, but signatures can be forged.