Hi,
Well, for the company I am in right now, they pay a percentage of
monthly personal/group volume. So if it is 0, of coz no bonus.
However, even if it is as low as $10 for that month, I still get
paid, even if the amount is tiny, and I personally can monitor and
knows that.
Another thing gd bout this company is that it offers another form
of bonus in that if i managed to make a downline reach a certain
successful level, even if a particular month, i got 0 for my MPV as
shown above, this other bonus will pay me a certain percentage
based on my downline's MPV, so I will still get paid even if that
month I actually bought nothing, as the company rewards
distributors for their past efforts too (in this case, helping
someone succeed) 
I understand that this differs from most companies which some have
to at least spend $100 or so for that month to receive any bonus at
all. 
cheers 