There is a fine line between scamming and taking advantage of a certain situation. For example:
A scammer offers to JV with you, and everything starts off on a good note, and you get paid, and send the scammer his share. Next month, scammer says he needs ALL the money earned that month to ramp up earnings, but really is just planning to scam you. I would say it isn't wrong to keep the money from that month and cut all ties with the scammer. But you have to KNOW he is a scammer.
There can be no room for doubt when you are playing with fine lines here.
To just outright be like "Hey man front me a $20 and I will send you $200 next month" is a no go in my books.