The correct answer to this open question is the following.
The hidden costs are the ones that are not often included in the final price of purchase. Corporations or producers have to pay for continual training of operators of fabric machines, or the maintenance of the equipment. That is a hidden cost.
Who pays them?
Producers could absorb part of those hidden costs, but actually, it is the retailer and then, the consumer, the client, who pays for those costs.