Many online dictionaries (including this one, that is dated as being printed in 1912) say that клюква
is a word for a church:
КЛЮКВА - церковь, часовня
КЛЮКВЕННИК - церковный вор; церковный карманщик
However it is hard to tell which word was "the original one" and which is "derived".
On this forum I found an interesting version why the thieves are called this way:
давным-давно заинтересовался, почему воров, специализирующихся на краже церковной утвари из храмов, называли "клюквенниками" (во времена до "без царя")- так вот, эти специалисты в темноте, не зажигая свечу, на язык и на зуб определяли, серебрянный оклад у иконы или нет!
Серебро кислит, как клюква.
So, the thief could tell if the icon setting (icon cover) was made of silver without using the light or candle. He tasted it with his tongue. If it had an acidic taste (as cranberry has) then it was silver.