On the box it clearly shows "solve the puzzle, unlock the reward"!
Not the case
Also, not needing a password once the gold has been claimed seems absurd, as there is no notice if the gold has been claimed and the store owners are not going to tell you if it has been. I can't be bothered to go in and check if the gold has been claimed and then collect my silver coin. Nice idea but its not working in reality.
"The adventure" should have had a lot more thought put into it before it went live. Spending more money to partake in the adventure (e.g text your guess) just seems like another way to make money out of us.
If the password system must stay in place then i suggest you set up a web page that you can type your guesses into that for whichever location you trying to solve, make it so only registered users can do it, that way you can track anyone abusing the system (IP/DNS logging as well). Being plain text it should cost very little to run (esp with bandwidth usage).
This would then stop the need to give passwords (or partials) to store owners and remove further leaks. Also I'm certain some stores must be getting tired of answering the phone to people wanting to guess passwords. In the London store they have to go and get someone (if they are available) to check a bit of paper to tell you if your right or wrong. Too much waiting around and hassle for me esp considering how busy the place is! Even then they have had the indiscretion of saying how many letters you have right, given enough time and guesses I'm sure you could work the password out via a process of elimination which is another possible way of circumventing the system.
Maybe try a hard clue for a gold coin and an easier one for a silver!
Thus far I have lost interest. Until a better system (one that not forever changing) is in place for partaking in the "Adventure" I am going to just wait for the next puzzle.
Sorry for the negative comments PUZZ but they need to be said.
The puzzles rock, thus far, the Adventure does not!