Buying gems
Mostly when just new stuff came out in the gem shop (Patches), The price will skyrocket or Plummet(Seen the plummet 2-3 times) , depending on the demand for the new items, best moment to buy is at a slow period. (Not many lately ,as there is alot of wanted stuff released in the gem shop)
it doesn’t go down.
it may budge a couple silvers after new patches… but no.