Keep a percentage of gross to go towards a deposit and don't remit payment immediately on new accounts. Imagine a 1K deposit wherein only $200 was paid up front and the rest was paid in terms of 2% of sales.

Further if you spend a week selling counterfeits and as it turns out that you make 800 usd in scam sales. The 2% towards deposits might only be $16 + $200 deposit but if the seller hasn't been paid out yet its trivial to claim the entire $800 in sales as the forfeited deposit.

The seller instead of profiting $400-$600 is now out $200-$400 in inventory and $216 in deposit with nothing to show for it.

The deposit needn't be ruinous. Just enough to make being a bad actor not worth doing.