scam employers

I have just begun freelancing. Earlier today I received an unsolicited project offer. The person wants me to be the virtual assistant for his art gallery, two hours per day. He seemed like he was sidestepping measures such as putting payment in escrow and really wanted to communicate via email. He said he was sending files, but they didn't arrive, and I haven't heard from him since. (Maybe I'm glad they didn't arrive.)

Now, a few minutes ago, a second person sent a second unsolicited project offer, almost identical to the first. I asked him about it, and he said it must be his assistant who contacted me earlier, but the email addresses aren't at all similar. Obviously I won't accept the second project, because if it really was his assistant, why would he want me to communicate with him separately?

Is this a common scam? Perhaps to send my computer malware, or to hack into my PayPal account? It seems anything is possible these days, and the first one already had me suspicious...

Maybe just insist on some sort of good faith payment upfront, or proof of his legitimate business (other than files sent by him). Does anyone have advice, or have you dealt with this before?