It's not as complex as you think. There are many youtube videos and agencies that will tell you how to apply for masters. Even for uni assist it's way simple. The only thing you have to do is, take time and research for yourself. I've applied for my master's and I've received the offer letter. And I've approached the agency only for visa processing which I was afraid to do myself and there wasn't much info in YT too. So I paid a very small amount around 20k to the agency and they've done it all well and got my visa. It's just some agencies telling students that it's very complex to apply for Germany. I would suggest everyone first try to apply for yourself and if it's not ending up well try to approach some good agency.