mutants players are a bug of the game? what do you think..

[Siddharth Singh]

If it's not illegal it's fine.

If upselling is bad then manipulation, tanking, farming green, rating manipulation, farming money etc is bad too.

In each of these cases you are taking advantage of the loop holes. Everyone hates upselling because it's not easy to do and takes a lot of time and effort while exploiting other loopholes is very easy.