Are you able to sell things at the venue? Like for example: pins, stickers, photocards, etc..

Last year at the Monsta X concert there were two girls giving away photo cards and if you wanted more than one you had to buy it (since I like 2 members I had to buy an extra one) there was also an older lady selling shirts and fans with the artist face on them. This was all before the event started so they were selling them out side of the venue while everyone waited to get in the building.

If you are connected to the event

Ur not supposed to.

I'm sure you could with approval

Pretty sure you can

yes

There's always someone walking around selling something here. You should be ok.

I would confer with the venue.

You probably need a permit and approval of the performing artist.