I'm looking into 3D-printing some props for a cosplay and stumbled upon a pretty handy listing on Etsy (if I'm not allowed to post the link, I'll edit it out).

Now, I'm a complete beginner to 3D printing and know barely anything, so I've got a couple of questions.

1. How safe is it to buy files off Etsy? Apparently, STL files are a little too large to be uploaded to Etsy, so upon making the purchase I'd get sent a txt file that includes a download link to the required files. Is that trustworthy?

2. Are there any file types that I should steer clear off for commercial 3D printing places? I've got a place to go in my city, I think, but I'm not sure if there are any limitations to which file types can be printed at all.

3. How likely is it that the arm prop won't fit? The listing does not specify if there are different sizes, and I'm not sure if they are even needed in the first place. In case it wouldn't fit out of the box, how difficult is it to scale the file to fit my arm proper?

4. How expensive would printing be? Probably hard to answer unless I know where I'm going and what they are charging, but I'd imagine the cost of material is probably not too high, right?

5. I think the seller also has the same files over on Cults 3D. Would buying there be preferable to Etsy for any reason (apart from pricing)?

That should be it. I hope my post is an ok fit for here - I'll post somewhere else if it isn't.

Thank you guys in advance!