how much potion can you sell before the market reduces the value

for context, i am selling potion (wont say what it is) with a significant profit margin (+1.5 mil every 990 potion) but i am afraid that if i keep trying to sell the potion. the potion will have less demand and make the potion lose value making me lose money. right now i am only selling the 990 potion and would like some advice on it.