COC/knowns (check on confirmation to known dealers) is standard operating procedure in the industry. If it wasn't, the business would grind to a halt.
Everyone on the 600-dealer system had to be recommended by someone already on it, and agree to pay within 48 hours, unless terms of the deal were otherwise. Violate that, and you're gone.
On bullion/scrap deals, COC meant as soon as you confirmed how much you're sending, the other party sends a check, and they cross in the mail. This also could be used for drop shipping, where dealer A buys from dealer B and the coins are shipped to dealer C. A sends B a check, and C sends A a check, while B sends C the loot.
After a run of uneventful transactions, the dealer I mentioned sent me the usual fast check, and it bounced. I went on broadcast and asked what was going on. Another dealer said he knew the one I was selling to was having money problems, just relax and he'd take care of it.
He drove 30 miles to the other dealer, said "Bigg Fredd's my bud, and you don't screw my bud." He picked up the $4000 or so in cash, and mailed me a bank check.
Think of it as feedback with teeth.
I had another dealer, in PA, who I sold a bag or two of silver a week. I'd call him friday evening and get a buy price good until monday noon. I'd buy over the weekend at a show(s), then call him monday to let him know how much was coming.
By thursday, I'd have his check, and typically, he'd have the silver. We'd confirm receipts on friday's call and do it all over.