How would you create a smart contract that allows for a commission?

Question

Let's say you were building a marketplace and you wanted to take some type of commission for allowing a user to sell a thing on your marketplace....how exactly does that work? Is there some type of template you can use that allows a person to pay you a commission, but then receive the payment for the sale of their item?

Answer 1

I don't know of any template, but this can be done relatively easily with solidity. Consider the dummy code below:

pragma solidity ^0.8.0;

/*your code here*/

// private function because it simply calculates commission and pays out accordingly.
// Inputs & other validation likely will come from somewhere else in the contract.
function takeCommission(address seller, address platform, uint256 amountPaid, uint256 commissionPercentage) private {
    // ensures the minimum amountPaid is at least 100 wei and is accurately divisible
    require(amountPaid % 100 == 0);
    // divide by 100 because commission percentage is expressed as a uint
    uint256 platformFee = (amountPaid  * commissionPercentage) / 100;
    amountPaid -= platformFee;
    payable(seller).transfer(amountPaid);
    payable(platform).transfer(platformFee);
}

Just knowing the commission percentage and what was paid lets you calculate it within a function, then you can call the .transfer() function twice with the respective values.