A word related to broker/representative beginning with C

Perhaps you are thinking of “in custody.”

From Investopedia:

Custodian

By ADAM BARONE

Reviewed By JANET BERRY-JOHNSON

Updated Apr 29, 2020

What Is a Custodian?

A custodian is a financial institution that holds customers' securities for safekeeping in order to minimize the risk of their theft or loss. A custodian holds securities and other assets in electronic or physical form. Since they are responsible for the safety of assets and securities that may be worth hundreds of millions or even billions of dollars, custodians generally tend to be large and reputable firms. A custodian is sometimes referred to as a "custodian bank."

I suspect you're thinking of "commodity", as in "commodity trader".

A raw material or primary agricultural product that can be bought and sold, such as copper or coffee. Lexico

An art gallery can hold your art on consignment.

Here’s an example (shouting in the original, unfortunately):

• SELL YOUR ARTWORK BY CONSIGNMENT Cooks Hill Galleries

Here’s the definition:

on consignment : shipped to a dealer who pays only for what is sold and who may return what is unsold - MW

The gallery sells the item as, in a sense, your agent or representative.

You may be thinking of escrow - it doesn't begin with a C but there is a strong C sound when pronouncing the second syllable, and it does fit your sample sentence perfectly: "The item is held in escrow."

Escrow is when an item or funds are held by a third party that will distribute them on behalf of the primary transacting parties in accordance with the terms that all parties agreed to in advance.

The term may be used in the context of various types of transactions including for example at auction houses, car dealers, and in real estate.