You will be calling people, and telling them that special "yellow" diamonds are all the rage, and that you can get good prices for them.
You will be telling customers that you can get them at wholesale prices, but misdirect by telling them the retail prices when it comes to selling.
If they dont sell, you will sell them at auction for them.
Either way, you make money from the commissions, not from any accrual of real value.
Good luck.
PS: if you take the job, let us know the commission structure. I have always been curious what the cut was.