Usage of 能骗就骗 (if you can cheat, then cheat)
能骗就骗 is a direct translation from a Cantonese expression "呃得就呃" (scam just because you can/ scam whenever you can)

It is a negative remark on someone's behavior; There's no encouragement of swindling 

Example sentence:

"戴條手鍊可以防癌? 仲要賣成千蚊? 唔好呃得就呃噃!" (Wearing a bracelet can prevent cancer? And it costs a thousand dollar? Don't scam people just because you can)

"條友呃得就呃, 千祈咪上當!" (this guy scam people whenever he can, don't fall for it)


  呃得就呃 is commonly used in Cantonese, but 能骗就骗 may not be as popular in Mandarin


As  AnnieFromTaiwan pointed out 能X就X is a common sentence pattern, so is X得就X in Cantonese. However, the instances you can apply "呃得就呃" to are so numerous, it stands out among all other similarly structured phrases and has became a 'common expression'