We also passively vote on the law by electing the people in charge of passing it. Why not also vote on the people interpreting it?
How else do you want to fill the position for a judge? By a panel of experts? Who decides who is part of this panel? Who decides what the selection process is?
Effectively there is a popular voting process somewhere. The debate is only where exactly in the chain.
I have not personally purchased files off Etsy, but the way you describe it this has clearly the potential for a scam.
I am not aware of any current attacks on 3D printers or the software ecosystem around it using prepared files. In any case, you should research what file formats the service you want to use accepts.
Since we all a little different, as you say it is unlikely to be a good fit straight out of the box. How easy it is to adjust the model depends on the type of files the model maker provides. STLs are basically finished models meant to be directly used in a slicer software to create the necessary machine code for production. Many slicers have basic capacities to scale or stretch models, but for complex geometry this is hardly sufficient for adaptations. For example, this maker included a project file for Fusion360 that is able to be easily adjusted via parameters. However, AFAIK it is not common for commercial makers to include a project file, because that's effectivly like giving away the construction blueprint for your product. Depending on the makers willingness they might provide you with an model tailered to your messurments.
That depends entirely on the volume and complexity of the model. Of course the model itself uses material but also support structure to hold the model while printing adds to the price.
As Cults3D as a commercial provider handels hosting of the files I'm personally much more inclined to buy there instead of Etsy with the promise to receive a link to the actuall files.
Just earlier today, I got a pop-up on YouTube about how they would block me after 3 videos because I use an ad blocker. Jump to now and everything is fine again. Thank you, uBlock Origin!
The answer depends heavily on your location. Where are you (roughly) located?