I have seen this multiple times that Sales users only care to fill in the monetary value of an opportunity once the opportunity becomes more concrete.
We can tell them that it's a better practice to already estimate what the opportunity will be worth but if they don't do it, there's nothing much you can do really.
Now, in a recent request, I needed to implement something so that the monetary value of an opportunity (the amount) needs to be know as from a certain stage and up. ("Negotiation" stage in this case)
I used a validation rule for this which worked well.
Now, I got a remark that for some products, it should also be possible to have a 0 monetary value...
So the question is, is it possible to know the difference between an opportunity where no amount was specified or if the amount that was specified was just 0?