It seems to me that the information that betting so heavily on FTX and SBF was an avoidable failure. So what could we have done ex-ante to avoid it?
You have to suggest things we could have actually done with the information we had. Some examples of information we had:
First, the best counterargument:

Then again, if we think we are better at spotting x-risks then these people maybe this should make us update towards being worse at predicting things.
Also I know there is a temptation to wait until the dust settles, but I don't think that's right. We are a community with useful information-gathering technology. We are capable of discussing here.
Things we knew at the time
We knew that about half of Alameda left at one time. I'm pretty sure many are EAs or know them and they would have had some sense of this.
We knew that SBF's wealth was a very high proportion of effective altruism's total wealth. And we ought to have known that something that took him down would be catastrophic to us.
This was Charles Dillon's take, but he tweets behind a locked account and gave me permission to tweet it.
Peter Wildeford noted the possible reputational risk 6 months ago:

We knew that corruption is possible and that large institutions need to work hard to avoid being coopted by bad actors.
Many people found crypto distasteful or felt that crypto could have been a scam.
FTX's Chief Compliance Officer, Daniel S. Friedberg, had behaved fraudulently In the past. This from august 2021.
In 2013, an audio recording surfaced that made mincemeat of UB’s original version of events. The recording of an early 2008 meeting with the principal cheater (Russ Hamilton) features Daniel S. Friedberg actively conspiring with the other principals in attendance to (a) publicly obfuscate the source of the cheating, (b) minimize the amount of restitution made to players, and (c) force shareholders to shoulder most of the bill.
I think my favorite version of this is something like "You can buy our scrutiny and time". Like, if you donate to EA, we will pay attention to you, and we will grill you in the comments section of our forum, and in some sense this is an opportunity for you to gain status, but it's also an opportunity for you to lose a lot of status, if you don't hold yourself well in those situations.
I think a podcast with SBF where someone would have grilled him on his controversial stances would have been great. Indeed, I was actually planning to do a public debate with him in February where I was planning to bring up his reputation for lack of honesty and his involvement in politics that seemed pretty shady to me, but some parts of EA leadership actively requested that I don't do that, since it seemed too likely to explode somehow and reflect really badly on EAs image.
I also think repeatedly that we don't think he is a good figurehead of the EA community, not inviting him to coordination forum and other leadership events, etc. would have been good and possible.
Indeed, right now I am involved with talking to a bunch of people about similar situations, where we are associated with a bunch of AI capabilities companies and there are a bunch of people in policy that I don't want to support, but they are working on things that are relevant to us and that are useful to coordinate with (and sometimes give resources to). And I think we could just have a public statement being like "despite the fact that we trade with OpenAI, we also think they are committing a terrible atrocity and we don't want you to think we support them". And I think this would help a lot, and doesn't seem that hard. And if they don't want to take the other side of that deal and only want to trade with us if we say that we think they are great, then we shouldn't trade with them.