Craigslist workers scam? help please?

I posted an ad on craigslist about needing a job. This guy named anthony cavallo messaged me about doing some advertising postings for him. I started talking to him over e-mail and messenger. pretty much he e-mails me the work to do for the day then i do it. He said the payment is weekley so i would get paid once a week and its $300. I asked him if i could get paid early this week by friday at least half the money and he agreed. How can i make sure the check is not fake or that he is not scamming me. He said he could do the payment however i wanted. via western union, money order, etc. I am worried that this is a scam. Has anyone ever been in this situation before? what should i do?