How often do the prices for the items in Join Avenue go down?

Question

I've noticed that sometimes the prices for the items in my Join Avenue go down by 10-100 Pokedollars or so. When and how often does this happen?

Answer 1

In addition to that, as you increase the rank of the shop, the areas will give discounts of 1% for every rank up you get. This goes up to a 40% discount. You'll also receive a 50% discount for a week when you make all eight stores reach Rank 10.

Source