DDownload is a scam service that steals money from their uploaders.
Uploaders lose their money, earning only 25% instead of 100% referral earnings.
DDL counts referral earnings only for 1 of 4 premium purchases by referral link. All other paid referrals in the referral list magically disappear after premium account purchase completed by them.

Their scam has been confirmed by several tests on multiple DDownload accounts.
During the test all DDownload rules are followed. Each time - there's new IP, new browser, and no cookies in private browsing mode.

You can find video proof of their scam on youtube by: "DDL PPS fraud/scam on webmasters".