I bet if you offered a large chunk of money to join up he'd suddenly have a spot for a new investor. People hate missing out on a good opportunity and scammers will use that to their advantage. The trick with a good long con is that the early "clients" actually turn a profit. These are the people who go out and recruit the bulk of your victims and will proudly defend you as you disappear with everyone's money.

Now of course this isn't guaranteed to be a scam but whenever you are offered guaranteed returns at an elevated rate like that, it's probably a scam or at minimum the risks are far greater than you've been made aware of.