PM me only if you are serious, and have more than 0.2 btc that you can trade with.
You might want to use an escrow for this or a 2-of-3 multisig address. The owner would send the money to them and then they'll pay you based on the profits that you made on your trade on a weekly basis.
I think this option is safer instead of allowing you to access the owner exchange account. There's no need for them to expose their email and password, they just need to give you the API access.
Yeah, showing his real portfolio/trade history might increase the confidence though.