How to deal the buyer asking for additional work!

[picvidpro]

One of my buyer, ordered me a 5 dollar video editing gig! He gave me 2 videos to edit! I charged 10 dollars, but he requested me to reduce price! I accepted bcoz I dont have any other order at that time! But when I delivered the output, the buyer asking for new updates which he was not mentioned in the beginning! But I charged him extra 5 dollars! But he told me that its a revision, you should do it! But I told him, its not a revision, its a new additional work which he dint mentioned at the beginning! But he got angry! Then I somehow accepted to do that additional work! Since I dont want to get the order cancelled, bcoz I did worked on the order half a day! But he took advantage of me and giving me the additional work again and again! I do have more than 120 five star rating in my profile! No negative rating till now! But I was afraid, If I get a negative rating bcoz of this buyer, that may end up in getting less orders in future! Can anyone help me how to deal with such buyers!