How does Taobao set the quota per person 1 piece?

Users can use time-limited discount service to limit purchases. The setting method is as follows:

When setting limited-time preferential activities, you can set the quantity that each buyer (according to the buyer ID) can take for each product, and the seller can set the time limit for purchasing quantity as 1 piece. Sellers can set it according to their own needs. The buyer's purchase page will also prompt each buyer's current "purchasable quantity".

When ordering time-limited discount function and carrying out time-limited discount activities, the seller can only set the limited quantity of goods purchased by the buyer.