Because of the potential overhang before the billing system catches up I think it would be appropriate to lower the service quotas on this type of account. I'm not sure if the customer can lower their own quotas which would be an alternate cost control strategy but a beginner wouldn't know to think of that anyway. The solution with billing alerts is good at a company level but too much for a beginner in my opinion.
I know unexpected costs were a concern for me when I started using AWS as a student in 2008 and it is still a concern for people in the same situation, just with so much more complexity on top of it all. It will be a tiny fragment of their revenue but as time goes on a higher and higher level of expertise is required to get started, even though you can accomplish a lot with just the free tier. The amount of progress they've made on this issue in the last 13 years is just not impressive.
They lock your account but keep all the resource active and the bill just keeps going up until you pay to get back in.
It's pretty easy stuff, IMO, but the upside for them is low -- after all they are already #1.
You can basically do max bill now -- you can set up a cloud watch alarm for billing and when it reaches a certain price, run a script. Your script could just shut everything down and delete everything, or do whatever is appropriate for your account. That's their solution to this.
Also they don't have instant feedback on usage -> cost. They batch process it. So if you get a huge spike in usage, AWS may not even know that for a while. They could in theory be willing to eat the cost of usage between it happening and their processing, but are probably unwilling.