If you really have the coins then move them to a good wallet that allows you to sign a message and sign a message to prove that you indeed have the coins. Or your action alerts a reg tag.
Indeed, I think calling out an escrow would give him chance to do transaction. Most new accounts are usually end up being a scammer but I dont judge the guy, maybe his real dont know maybe.
If I go with my instinct then I will say this is 100% scam approach. I highly doubt someone with that many bitcoin will come to a random forum and will make a like of post to sell his bitcoin. And look at the platform he asked to trade. Why would anyone give a Jackass about a specific platform with having over a million dollar worth of bitcoin.
Everything ends up with a conclusion that this is not a real deal.
If a new user sprouts up from the blues which such huge amount of bitcoin seeking for buyer from just a random platform
So am standing on my grounds agreeing with @bitcoingirl.com on this ever issue that the above mention posts from every speculations looks suspicious.
Thanks.