They're 3D printed, so really it all comes down to the printer.
What kind of printer? What kind of resin? What print resolution? etc.
The printer will be able to scale stuff up or down at request normally. For stuff like this I'd suggest going over to Etsy instead of eBay - as you can see picture reviews of stuff, meaning you can normally see what kind of quality people are receiving from the various printers.
A 3D print could be anywhere from:
-Poorly calibrated machine printing quickly in cheap FDM/thread...
-Perfectly calibrated machine printing slowly in expensive/nice resin...
So it's entirely up to the printer. Now, I have discovered very quickly that many 3D sculpts are not very gaming/miniature friendly, so I try to find companies or designers who actually print their stuff at playable scale. A lot of 3D sculpts are designed like art...with details or components that simply do not scale well when printed smaller. I've had some 3D printed miniatures where the details were so fine they broke if you glanced at them sideways...mainly because the 3D sculpt was probably intended for larger use, etc.