Pig in a poke refers to a kind of scam in which sellers vend goods to buyers while keeping the nature of the goods hidden from the buyer until after the purchase is complete. And there is no 'money back if not satisfied' provision on the sale. The scam originated in Europe during the middle ages, when during times of food shortage merchants would put a dead cat or dog in a bag and sell it to buyers as "pork." Someone who knowingly engages in pig-in-a-poke scams as a seller is usually considered a cheat or a fraud. Someone who does so as a buyer is usually considered a victim on the first occasion, and a fool if he becomes a repeat buyer.
Most of the offers by KABAM to sell valuable game items inside of chests, most of which contain items of far less value, are pig-in-a-poke scams because there is no way the buyer can knowledgeably estimate his risk. If KABAM would publish the odds of getting each of the possible items that might be in a chest, then it would be possible for buyers to make a risk-benefit analysis, and then the sale wouldn't be a pig-in-a-poke because the buyer would be informed, at least, of the odds for success.
Since gems are usually (with exceptions) bought with real money, it looks as if KABAM has an obligation to supply information to buyers regarding the probability of finding, for example, a +7 Master's Token inside a Bors Chest, as well as the probabilities of finding +5 or +3 Master's Tokens or a paltry, almost worthless "lucky token." So it would be a good thing for KABAM to provide the percentage odds for each of the possible items that might be found inside chests.