Been offered a Domain, how to ensure it's not a scam?

I've been offered a domain which would be a decent addition to our domains, but how do I ensure the vendor is genuine?

I was approached by unsolicited email via our contact form on our existing site, very similar domain to that which is offered, and he's put a 301 redirect on the domain for sale to "prove ownership" - could it be a scam?

They're not asking for much, around $500, and have offered to sell it via the domain host (who i've never heard of) via their marketplace - marketplace.epik.com)

Should i demand to do Escrow or how else to make sure i don't get scammed?