I get the rumor but it's not as if GG is a small bodega who buys supplies at Costco. They have distributors and wholesalers to handle this.
Well, I happen to know as a fact that they do sometimes get Romain from Costco.
Sometimes their supplier sends them lettuce which is too infested to clean. They return the shipment and try a different supplier or batch. When Rabbi Green was there, he expertise was where to get the best product from. Rarely, he had to go to Costco. Sometimes it was good enough. Sometimes it was not. When it wasn't, he ordered from Postive and repackaged. This was a rare occasion.
Rabbi Green is not there anymore. This new guy has been more often than not using Postive. But it would not surprise me that he does not no how to order from which suppliers, and he therefore went to Costco.