It depends on what you believe is greedy.
In the prior system, paypal takes the risk, if no sale occurs, they work for free.
Now, the seller and buyer will take the risk. Since paypal does work regardless if the sale finalizes, they always gets paid.
If anything this is more fair to paypal.
We can't predict perfectly what's going to happen. But overall, as seller, you have options to build the risk into the price. This would include the situation you mentioned where people will successfully dispute the cost.
If you expect 1% of people to do it successfully, you just take that 1% and divide it into the base price.
If you're worried about the deal not reaching MOQ, then write the condition of partial refund plainly in the invoice, the forum post, the seller communication , etc, such that if dispute does occur, you have a firm stance.