Well, what do the duty declaration and duty tracking sticker say?
At least over here there ought to be one that tells you what the seller declared the goods and their value as, and another that tells you either the specifics of the duty fee calculated, or one with a large (over here) letter+number combination that tells you which standard category this falls under (usually for duty free packages).
50 on 300 is is ~17%, so that’s a pretty normal duty depending on the goods and which country they originate from.
None, and that’s probably a good thing. And also really not unexpected given how small the platform is.