As someone who helps deliver a free tier to customers at my work, I can sympathize with Microsoft’s pains here. It sucks the author had such a bad experience, but fraudsters are scammy bastards who are ruining “free compute” for everyone.
Does that mean there are people out there who'd sign up for a free trial but who have no intention of paying for any product, ever? Wow*
(This is a genuine question) in the spirit of scientific enquiry, that would appear to be far more of a problem with your marketing department and their assumptions about converting trials to paid, rather than with the people who have no intention of paying for your product?
* not really
The fraudsters and miners, however, are a whole other thing. They will suck up the maximum amount of resources they can and extract a tiny profit from it. It will inevitably cost you, the cloud provider, money, because mining typically isn't profitable without GPU compute anyway, so the entire profitiably of what they're doing is based on the fact that you are offering free electricity. It's a net loss, as these users will also probably never convert proportional to the usage they incur. Most users of free tier services use a tiny fraction of the available free resources within the tier. These guys will hover at 99.99% always, ruining the whole profitability model and dramatically increasing the cost of acquriing a customer via free tier.
A lot of cloud services (not just Azure, but certainly in Azure) are assigned a globally unique resource name, which also gets assigned a DNS name.
Domain squatters can walk the domain to find these services and keep an eye for if they lapse. (Sometimes this happens if a service needs to be recreated due to upgrade)
What a malicious user can do during that maintenance is trigger a deploy of the same service name now that it's available and snap it up. They can either shut down the VM or scale down the service to be sitting there and not costing them anything, and see if they can extract payment from their victim to release the domain (which might be hard coded somewhere). Worse yet, they could leave it as is and try and see what interesting traffic starts coming in and tinker with it.