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 disagree with this. I think we should receive money from basically arbitrary sources, but I think that money should not come with associated status and reputation from within the community. If an old mafia boss wants to buy malaria nets, I think it's much better if they can than if they cannot.
I think the key thing that went wrong was that in addition to Sam giving us money and receiving charitable efforts in return, he also received a lot of status and in many ways became one of the central faces of the EA community, and I think that was quite bad. I think we should have pushed back hard when Sam started being heavily associated with EA (and e.g. I think we should have not invited him to things like coordination forum, or had him speak at lots of EA events, etc.)