How are you going to actually SELL something stolen from a temple?
Far enough away from the Snake God's temple, and thus influence, there'll be collectors who have no worries about Snake God vengeance. Alternatively, more chaotic followers of the god would pay well to get some True Relic of their deity upon their own private altar, without worrying too much about the fact that it was taken from a more lawful sect of the snake-religion. Mongoose God followers could want it, first of all to deprive the Sake God followers of it, secondly to officially desecrate it. And all kinds of other possibilities, as well as those mentioned.
Coins weren't valuable because they were stamped with the king's vissage.
In some ways, they were. The visage, or other official mark, that was stamped upon it was intended to give the people handling it the reassurance that it was gold (or whatever other material it was supposed to be) of the specified composition. If it also weighed what it should (or you had a given weight of coins equal to what you wanted, even if they were individually underweight after shaving) then you could in principle accept it without having to get your local alchemist or other relevant metallurgy expert to scrape bits off and test them. (Imagine every time you got change in shop having to scrape a bit off of the coin to test, and when you paid them back into another shop they did the same, and the next person to receive them then had to...)
In practice, coins were adulterated at source by various rulers, and other tricks, but as long as everyone
treated the coins as worth what they were supposed to be then wider trade throughout the land could be conducted without too much concern. The problem was mostly regarding international trade, or other situations where multiple coinages could be used, in which there would be a legitimate reason to say "Your coins aren't worth as many of my coins as they used to be, I demand more of yours/will give less of mine for this trade".
There were some attempts to peg currencies to various standards, but they caused such situation as mass export of silver coinage from Britain and import of gold coinage into it, due to an imbalance of relative trading values internally and externally.
But the visage/other symbol is a long-established principle. Even for money that's not actually worth what it represents, like clay tokens reflecting the value of number of cattle from ancient times, often sealed with others into a clay 'pouch' similarly marked with a total number of the cattle supposedly contained. Obviously these could only be used if produced by a trusted source and could not be forged as such by others, but that's an eternal problem.