Its strictly stated that paypal masspay can not be reversed also the maximum fees on the senders end is $20 so can send $10,000 for $20 through paypal.

The conditions for it though require you to have actual paypal funds in your account balance and it needs to be an unlocked payment form by calling customer support. I've accepted masspay as a payment otioin for digital goods since 07 and haven't had a single case yet where I seen a paypal masspay reversal.