With most devices that sample NetFlow, there is an export of the sample rate in the flow record or an option template. The collector then uses that sampler information to multiply results (packet and byte counts) to arrive at traffic use numbers that more closely reflect actual bandwidth use.
sampled NetFlow configuration
I have been working with a number of customers recently who are required to use sampled NetFlow because of vendor configuration rules. In just about every case, reporting accuracy from sampled NetFlow has been a major concern.