Notably, Jessica says in the Less Wrong comments that "GiveWell is a scam (as reasonable priors in this area would suggest), although I don't want this to be treated as a public accusation or anything; it's not like they're more of a scam than most other things in this general area."

I do not find her evidence very convincing. Some of it relates to private information which she privately messaged to Jeff Kaufman. The first part of this private information, a rumor relating to GiveWell's treatment of an ex-employee, was disconfirmed by the person in question according to Jeff. The rest of this private information is advice to talk to specific people and links to public blog posts.

The rest of the evidence seems to center around arguments that international charities like AMF create dependency and apathy, sourced from a YouTube philosophy video creator and apparent worker in international development who cites personal anecdotes and Dambisa Moyo's book Dead Aid. This person alleges that AMF and other organizations have put the local bed net makers out of business and says that he has personally seen many families that only bring out their bed net when the AMF inspector comes around. Jessica emphasizes further that the strongest section of the video is where the he says that (quoting Jessica) "the problems caused by aid are extremely bad in some of the countries that are targets of aid (like, they essentially destroy people's motivation to solve their community's problems)."

Arguments about dependency and building sustainable institutions instead have been discussed a plenty in EA circles over the years, and I won't rehash them further here. I just want to note that Moyo says herself that her critique should not be applied to private NGOs, and even aid critics accept that health interventions, like those of most GiveWell top charities, can have positive impact.

I also do not think that, even if the evidence was rock solid, this would mean that GiveWell is a scam; people can be wrong or disagree without it meaning that they're scamming you or that they're deluding themselves.

Edit: Cleaned up a couple of sentences

If you didn't see it after two read-throughs, I don't think I'll be able to make a summary that conveys the relevance.

Maybe these excerpts draw it out a bit?

Worker: “Do you think any charity other than us would have run the calculation we did, and then actually believe the result? Or would they have fudged the numbers here and there, and when even a calculation with fudged numbers indicated that the intervention was ineffective, come up with a reason to discredit this calculation and replace it with a different one that got the result they wanted?”

...

Carl: “Why don’t you just run a more effective charity, and advertise on that? Then you can outcompete the other charities.”

Worker: “That’s not fashionable anymore. The ‘effectiveness’ branding has been tried before; donors are tired of it by now. Perhaps this is partially because there aren’t functional systems that actually check which organizations are effective and which aren’t, so scam charities branding themselves as effective end up outcompeting the actually effective ones. And there are organizations claiming to evaluate charities’ effectiveness, but they’ve largely also become scams by now, for exactly the same reasons. The fashionable branding now is environmentalism.”

...

Carl: “How do you even deal with this?”

Worker: “It’s already the reality you’ve lived in your whole life. The only adjustment is to realize it, and be able to talk about it, without this destroying your ability to participate in the act when it’s necessary to do so. Maybe functional information-processing institutions will be built someday, but we are stuck with this situation for now, and we’ll have no hope of building functional institutions if we don’t understand our current situation.”