So to be clear what you want is a 10% tax on trades and vending that is intended to fall on the buyer? I think it would need to be visually clear that there's a tax and I'd prefer it to be 5%, but there are other hurdles that first need to be tackled.
I vend essence for 90k. I lose my essence and get 90k, the buyer loses 99k and gets essence. Works fine.
I trade essence of 90k. I put in essence and the other person puts in 90k. Is the game going to take 10% more from the other person and is that going to be clear? How could that be programmed and would it make sense with the current trade system? Since the two are in a trade won't the person buying my essence demand a lower price because of the tax? This wouldn't happen in vending because one of the parties is afk.
The trouble with the charge being on the buyer is that it only works through vending. You could say that's fair because people who are active in the market are getting better prices, but the market is too small for that to work.