In Ocean's Eight (2018), Debbie explains Tammy how she fell for Claudie Becker:
Debbie: Lou and I were going through a rough patch, and I really wanted a big score of my own.
Tammy: So he roped you in?
Debbie: Mmm. Not really.
Tammy: What, told you the truth?
Debbie: Only way to con a con, right?
What does "Only way to con a con" mean?