When the sale happens, record the full amount as income, then immediately book the artist’s share to a Commissions Payable liability account. That keeps your books clean and clearly shows how much you owe at any time.
Deposit from sale -> Debit Bank (full sale amount), Credit Income (full sale amount). Then, create a journal entry: Debit Commission Expense (or COGS if you prefer tracking it that way) and Credit Commissions Payable for the artist’s portion.
At the end of the month, when you pay the artists, just cut checks or record payments against that Commissions Payable account. That zeroes it out and properly reflects the expense in the period it’s earned.
For Square fees, you can either record them directly as a separate Merchant Fees expense each time a deposit comes in or use the Square Clearing account method, depends on how detailed you want to reconcile.
Robin Kon