collect payment before the art is even started, set expectation that said art might take at least two weeks. Two weeks is standard waiting time for withdrawal to a debt account. Once its out of paypal, other person cannot chargeback, paypal will not refund the money from their own pocket unless from ebay protection.

Basically dont start or finish said art until payment has cleared the basics.

When getting people to pay, make sure you understand what option you get them to choose in paypal, EG gift, payment owed, etc. This can affect waiting times for receiving the money depending.

Do not accept payment from non-verified paypal accounts. Instructions on how to check if it is verified online.

I have no idea if this works, but I have seen A LOT of people get customers to put binding statements in the paypal sent money message thing. Usually something along the lines of "I am purchasing a digital service for the creation of digital art. I will not charge back..." Etc etc etc.

Lastly another quick semi-related thought, if I remember correctly, the basic rule of ownership in commission content creation, no matter what they get you to draw, unless the artist signs a contact or has some form of release, the artist always own the artwork, and the commissioner was just paying for the service.