This may be a rare occurrence for most hubs but I’ve had instances where a customer will upload a single file to be quoted but the .stl file will contain multiple parts to print. This can allow the customer to bypass startup costs for different models and the quote will not be accurate.
(I realize this problem can never be solved 100% since you could connect two models with a single line and claim they are now one part.)
I’m wondering if there would be a way to add a step to the .stl pre-processing that verifies there are not separate parts in a single .stl
You can use cura to split the parts and upload them individually to the order before accepting if the fee is the issue.
I’m not sure there is a perfect solution, since many of the people uploading “plates” of parts are downloading them from somewhere and tend not to be terribly experienced as designers.
Sometimes I like getting plates of parts because often each plate is one color, sometimes they are terribly laid out.