If you get two or more FB from the same buyer in a short period of time* they will count as one.
Does that help?
FWIW, feedback is voluntary. While FB for buyers can only be positive, it is more important for sellers.
Even there the only ones who look at FB are future customers (so keep it calm and professional) and auction sellers (who check the FB buyers leave for others for red flags).
*I don't pay much attention to FB, so I don't have the numbers at my fingertips.