After completing many coin offers and spending many hours building my collection, I was banned without explanation. I also have a completed offer that I never got my 1.3 million coins for. After many days I was told I violated terms of service, but was not given an explanation how. I guess it could be summed up in the fact the game Support is very very poor.
Sahdali about Quidd: Digital Collectibles, v1.10.5