In what sense is Costco an "abusive" company? They squeeze their suppliers, but their suppliers legitimately have other options. I'm not aware of any market what Costco is the only game in town.
I can see this both ways. Obviously, nobody is forced to sell to Costco, Amazon, or Walmart, but in a business with thin margins, like Retail, the only way to stay afloat is to sell high numbers. A quasi-monopoly does force vendors to comply in a way.
Costco meets no reasonable person's definition of monopoly. Not quasi, not sort of, not anything. They do a couple hundred bill of sales in a multi-trillion dollar market. Sub 10% share.