Question about scams on craigslist?

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so i put a post on craigslist yesterday saying that i was looking for work. Nothing big, just yardwork, or cleaning, or whatever someone needed help with. I also put in the add to send me their phone number and id call them the same day. Ive gotten a few e mails saying they are paying $1,200 a month, or $500 a week, to have packages sent to my place, and im supposed to mail them. And to go buy clothing and other stuff, and they are paying me up front. I know its a scam, but how exactly does this scam work? And how are they actually gonna rip me off? anyone deal with these people before?