Image source

Other examples from the web:

• Watch out for that girl with the red hat and don’t believe what she says. She’s a slippery customer.
• He’s a slippery customer, that Tim, I’ve never felt comfortable with him.

Watch out = to be careful; to remain vigilant.
To snatch = to take something or someone quickly and suddenly; to grab.
Untrustworthy = not able to be trusted.
Cunning = getting what is wanted in a clever and often deceptive way.