Vending (Seller's Kiosk) Questions

First of all I just started playing seal online and I am currently in a guild. This is where my question starts:
I bought 2 rubies for 800k and tried selling both for 950k - but somehow I do not think I am getting profit out of this and I have heard rumors that using vending (seller's kiosk) reduce the price of an item when it has been bought by other player by around 5-10% and in addition you also get 10% tax and this 10% tax goes into the guild bank because I am currently in a guild.

It's 5-10% + 10%

Is this true? Do seller's kiosk and being in a guild give the player tax?

This bothers me because I am not getting profit out of this.

i think there isn't 10% tax goes into the guild bank

Nothing to do with guild, all my characters are guild-less and none of them recive the full seller-price.
Money get lost somewhere along the way in a secret tax or some sh1t that YNK doesnt let us know about.