Doubts for upcoming MagicCon in Amsterdam about selling

Hi!

As the title states, I've a few doubts regarding the upcoming MagicCon at Amsterdam, especially about selling cards.

To give some context, I'm not looking to sell a big collection of cards or anything near that, it's just that over the last 3 years I started playing Ive definitely pulled some cards, none of them worth over 40, but altogether could get me a few bucks. The ones I'm willing to sell probably would get me over 200€, which is not much but they're definitely not doing a lot sitting in my binder, so figured it'd be a decent place to do it at. Besides these cards I also have two precons I bought at the time and barely played and looking to get rid of (Eldrazi Unbound and Necron Dynasties)

From what I've gathered vendors tend to offer mediocre prices (Ranging from 50% to 65%) or slightly more in store credit which I'm not actually sure I'm interested in right now, something might catch my attention at the event but I'm not searching for a card specifically as of right now.

A doubt I have and I haven't seen resolved somewhere else is, is it licit to sell cards to players who just happen to maybe want to be interested in anything I've in my binder? Like, would that get me into any trouble if someone finds out? Or is it a common practice and it's not frowned upon? I obviously don't want to get into any trouble and since it's my first time attending I've no idea how that turns out.

On a side note, is there any place I could post the cards I'm selling for people going there? Didn't want to do it here since I know this is not a marketplace, was just looking for info.

And lastly, this is totally unrelated, what bracket decks do most people bring to the commander pods at the cons? Is it mainly bracket 3 I'd assume? What has been your experience?

Thank you very much for you help!