I read a report of this in a newspaper which said they had tested "400 seeds" from each supplier. I think this means they tested about 8 packets of seeds from each supplier. I think that is far too small a sample in order to decide which are the rogues and which are the reliable suppliers.

The fact that who were the rogues in relation to "flower seeds" had very little correlation with who were the rogues in relation to "vegetable seeds" suggests to me that the results had a substantial random factor arising from it being a poorly designed experiment of little statistical significance.