What is a buyback price?
The buyback, or bid, is the other side of every quote: what the dealer pays you for the same product on the same day. Every dealer has both prices; not every dealer volunteers the second one.
For standard bullion, bids are competitive and close to spot. For heavily marketed premium products, bids can sit far below the price you paid, which is precisely the information the sales process is designed to keep you from seeing.
Why is the buyback the best transparency test?
Because it can't be spun. Marketing can justify any purchase price, but the buyback number states plainly what the dealer believes the product is worth. The gap between the two prices is the spread, your true cost of the round trip.
A dealer confident in its pricing publishes an unconditional buyback policy: we'll buy back anything we sell, any time, no fees, no minimums. The absence of that policy is information too.
How does buyback show up in practice?
Before you buy, ask in writing: 'What is your buyback price on this exact product today?' Compare it to the sell price. Then ask whether that buyback policy is unconditional, and get that in writing too.