The premium chest has no guarantee; It states that it COULD hold many rare items, which is quite clearly no guarantee.
(The other chest, in addition to the unique chest, with a guarantee is the Fancy Chest, which guarantees value above 5000.)
It then listed multiple rare items in order to entice more people to buy them. As I've said and a few others as well, it would have been nice to know that it was also possible to receive not so rare items that were available from doing a few simple tasks such as the young stallion which you get from the tutorial quest or the sled which you could get from either the advent calender or praying ten times, or both.
Given that it's called a premium chest, and it cost me $27 real cash (so could people stop harping on about this all being about nothing because it's all in game cash), I would've expected the items to actually be rare. The definition of rare is what's being questioned here as it seems that Inno just lumped anything that you can't buy in the shops into a premium chest and it's pot luck what you get.
Here's a few stats from
http://tw-db.info/?strana=item_stats though:
66.46% of inventories (42273)have the young stallion
39.63% of inventories (25203) have the sled (30978 items in total and they're non auctionable)
41.24& of inventories (26228, 40047 items total) have the Huckleberry Slingshot
43.94% of inventories (27939, 37792 items total) have Granmont's Pistol
These are items that I'm aware of that people, including myself, got in a premium chest. Would you call these items rare? I would not. Items such as Pat Garrett's jeans or General Grant's Saber are not even in 1% of inventories, and the description of the Premium chest gave me the distinct impression that these would be the sorts of items (and the only sorts of items) that would be available from these chests. Whether the word 'could' is in the description is irrelevant. The rest of the description was intentionally misleading in order to make us buy one