Checking for fraud

Last year I had a lot of fraud orders so I'm a bit shy this year. One frauder placed 3 big orders last year before I got a chargeback. Then in January I got a chargeback from a December order. Person said her husband thought it was fraud, but the money was still lost in a chargeback. So now this year every large order makes me nervous. Is there anything I should be checking? I use PayPal for payments.