Because, his weekly payouts is never greater than than the contract selling profit.. He made nearly 100-150 BTC profit in a week. I am calculating the income for about 3 months, and weekly profit never drops below 75 BTC per week..
Um, HOW has he made such a 'Contract Selling Profit' please ?
If it is a Ponzi then there'd have been next to no actual mining taking place unless you're saying he's invested all of the BTC from the most recent contracts into some mining Pool somewhere ?
OR
His algorithm was complex enough to make sure it rarely if ever made it to 100% ROI and so it could safely repay the Capital without him being 'at risk' so-to-speak ?