Using the word 'Scam' here is not right in my opinion. Some great points raised by katakatica above.
Also, Fiverr is not the right platform to be polishing your skills from advanced level to expert level. There are so many other professional websites like Coursera and Udemy where you can polish your existing skills and take them to the next level and they don't charge exorbitant fees for the courses either. Fiverr is a platform for freelancers and they offer these courses for beginners which you can enroll yourself in.
I hope and pray the points raised in this thread justify your concern.