Back when the liver eater brought his plews in were there more than 1 buyer?

There were multiple traders at most of the big rendezvous in the Green River area. Each fur company typically sent its own train of goods. And there were sometimes also free traders.

Company trappers were required to "sell" their furs to their employer. Free trappers could trade with whoever they wanted.

The golden days of the fur trade were gone by the time John (Jeremiah) Johnson got to the mountains in the late 1840s. There hadn't been a real rendezvous in years. 1825 to 1840 for rendezvous. He likely sold his furs at local trading posts. In later years there is record of him making a portion of his income as a woodhawk, cutting firewood for the Missouri River steam boats. . He also did some scouting for the Army. During the Civil War he fought for the Union in the Western Missouri Campaigns. He also, along with a character named X. Beidler reportedly made whiskey and sold it to Indians. Spent his later years around Red Lodge, Montana and died in a veterans home in Los Angles in 1900 at the age of 75.

You sure about that K?

I am aware of that happening a couple of times but was under the understanding that it was usually just one company present.

There were 2 main company’s competing for the fur. American fur and another ( forget the name) I think one was owned by John Jacob aster and the other by the Sublett brothers. Also some competition from Hudson Bay company. Usually the first to arrive at rondevous ended up with most the free trappers fur.

American Fur Company was Astor's company. Sublette's was Rocky Mountain Fur. Hudson Bay never appeared at a Rendevouz. They collected fur with brigades or trading posts and packed them out to the Columbia.

There were multiple little companies, and partnerships, that brought small loads of goods to the rendezvous.

Gantt & Blackwell, Nathaniel Wyeth, Bonneville, Bernard Pratte & Co., Joshua Pilcher and Stone & Bostwick are several of them.
They were never true competitors to the big guns of Henry, the AFC and the RMFC. Some were just big enough to be a thorn in their sides.