The app was working, during review. Then once approved its behavior changed and the scam started.

This is trivial to implement and done by many developers.

Apple doesn't approve each release of an app?

They do, but in these cases the binary never changed. A value returned to it from a web API changed, or a date passed, or the users are outside of Cupertino, etc.

Are there any automated approaches to solve this type of bait and switch?

When I first published my app, they asked for a video of video fully working. Then once I had a bug and they sent me a video of it with the steps to the bug. So there are definitely people opening and testing apps

Yeah, same here, the only explanation I can think of is that the scammers have someone on the inside approving these fake apps.

No, the reviewers never see the scam screens. Once approved the scammers change a setting in the cloud and the app starts opening in scam mode.

If the app is working properly during review, why change it to nonworking later on?

It is like that Key and Peele skit about robbing a bank by working there.

If you can create a working app why not leave it as is ?

It was likely a very poor keyboard. Just operating well enough to pass review. Once a user saw it, no one is buying.

The more boring reason: some review employees are bad at their job

Given the up-and-down, seemingly always controversial (and sometimes adversarial nature) of how Apple performs their app reviews and enforces their rules, I think it's 50% on lazy/bad reviewers and 50% poorly-communicated rules and regulations.

I wonder if there are a load of failed submissions too. They'd want to minimise effort so I guess they'd have good ways to quickly rebranding an app as a new one.

Or the app talks to a remote server so it works normally during the review period, but after the app gets approved the author changes a flag on the server and the app changes to "scam mode".

And this is another example of why Apple is too focused on short-term profit over long-term user experience. I think we all know that the app reviewer's top priority is making sure the monetization strategies in the app are "compliant".

Whether it works or not probably won't get you fired as an app reviewer. But miss some IAP workaround that an app is using and I'd bet it could be your job.

You’re exactly correct and is why Apple should be taking action on this problem — it’s in their long-term self interest to do so.

Having customers distrust their App Store is really bad for them in the long run, and would be a competitive advantage over Google if their store was less crammed with garbage.

As it stands now, I usually find apps by looking for solid reviews outside of the App Store app, and am very wary about purchasing anything.