Dealer A sells chip graded a guarenteed MS99 to chipper B
Chipper B should ask for Certificate of Authenticity.
Chipper B puts chip in collection and cert where it will not be lost.
Chipper B desides to sell chip to chipper C. Can't find cert but guarentees C that dealer A wrote one.
Chipper C gets hard up for cash and takes chip to dealer A. Dealer A says it is a MS90 not 99. Chipper B shows up with lost cert. Dealer A says I wrote it but this is not the chip I sold with the cert.
Chipper C takes chip to Dealer D. Dealer D says it is a MS80 chip and dealer A must be blind if he wrote that stupid cert. Dealer D says "Always buy from me and I will guarentte the chip and give you a cert, no one will doubt."

I personally guarentee the chip in this story was the same chip at all times.

No thanks James, I like the hobby too much to see this happen.
Put a price on your chips. If I like the chip and the price I will pay it.