Setting up a (side) business around grading cards?

I’m wondering if it would be possible to set up a real side business around grading cards? I’m located in Europe though, so I’m not sure if all US answers would really apply, there’s a few thins I’m struggling with, I’ll list them here.

As I understand normally business that buy/sell goods from suppliers to customers pay 21% VAT/tax when buying from the supplier and in the end add 21% VAT to the final sale price. It doesn’t matter a lot because all their competitors are businesses and thus everyone shares similar costs.

It gets more interesting with grading cards though and there comes my confusion. For purchase I either have the option to buy it from Europe, if I buy it from a non-company then I don’t pay taxes, if I buy it from outside Europe then I need to pay taxes on import (even if bought from a non-company) or I can mark a low value but that’s not really legal I believe.
And then when selling I would need to add VAT too? But I compete against other sellers that don’t need to care about having a business as they are private collectors.

I’m a bit hesitant to ask for more information from the tax services as then (maybe paranoia) but they might make a fuss about my personal collection and selling/buying I do for that sometimes, so I’m hoping that somebody can help me with this. I understand that this post is a bit vague but I can’t find a way right now to write it down in a more clear and concise way. Of course experiences from strictly US businesses are welcome too!

If you want the most accurate information I think you were on the right track by discussing it with your tax agency. You can do it incognito. At least then you’d have the legal base and can go from there.