If you ask is freelancing scam? I will say absolutely not. Actually the matter of fact is that the field itself is not scam. Websites that work as freelancing platform are intermediate sources and they offer only their service in return of meager fees. The clients or customers, with whom you work, can be scam. So there are proper rules to follow when you start working as freelancer and asking for milestone before working is one of them.
Suppose, you are working on a platform like freelancer.com. I ask you to do a project of data entry, lets say adding some data to excel file. I will post a project and hire you as a candidate to complete the work. Once you complete the work. I don’t pay. Does that mean the website is scam? No it means I am a scam and you must take specific steps for ensuring you get paid. The term milestone is used for that specific step. Some websites use term Escrow for this system. When I will post project and hire you, you will ask me to create milestone or escrow of full payment which I will give you when you will deliver the work. This payment will be kept by website and when you will complete the work, it will be released to you. You can read about the concept of milestone in next posts.
So working on a platform is actually not a scam, employers who post project on that platform can be scam.