Mobile app development is a relatively young industry; and as such, it still has a number of pitfalls that are scarcely documented. Multiply it by the number of main platforms, and then by a huge number of frameworks (more or less elaborate), by the incalculable quantity of changes in the platforms themselves (not always described in details, and mind the support of older versions)! Thereby hangs also the fact that despite all attempts of testing automation, there are still some gaps that require handwork. Thus, we have a certain number of situations when even a well-seen expert might have an egg all over his face…

It is especially typical for in-app purchases. Often we encounter ineffectual monetization libraries, mobile Internet lags, card online payment whims… which logically gives us an undetermined process as a result. Still we shouldn't be tragic about it, as most peculiar cases are basically caused by rather simple mechanics – and that's what is explained in this paper.