First thing is to reassign the business checking account to all the third party payers so that funds go where they are supposed to.
Second thing is to not wait until it is tax time to review your accounting to see if it is right.
You will have to do the research to find the item names, then do an inventory adjustment, set the adjusting account to COGS and lower the qty of the items sold.
You should be booking the total amount of the sale, and reducing that amount prior to deposit by the fee's and shipping charged by the third party sellers. Typically folks use a sales receipt to record the sale of inventory items to a generic customer, etsy, shopify, etc. Paypal and venmo are not sellers, they are basically checking accounts holding your funds.
If you do the sales receipt on a daily or at least weekly basis, create a service item that links to the fee expense account, and another that links to the shipping expense account. List the items sold and the retail amount, then follow that list with the fee item, set the qty to negative one and the amount of the fees... Do the same thing for shipping expense.
