It's prior and post accumulation in some counter or for display purposes. So at the moment the like is done it is possible to distinguish between fake and real but after you collapse them into a single counter you no longer can distinguish fake and real.

This is what gives the 'fake likes' their value, that they are then used by Instagram in exactly the same way as real likes. Instagram clearly fails at distinguishing the two, so you really can't fault the users for not being able to do so either. The fact that this service is available and apparently works is a pretty strong bit of evidence that all likes should be distrusted but that's not how it will play out.