Detailed Instructions: Given a text, write a compressed version of it in a single sentence.
Q: Second, most firms gather sales data, not demand data. Customers rarely inform the sales clerk in a typical retail store if a desired product is out of stock; they either buy a different product or leave the store without making a purchase.
A:
Firms gather sales data not demand data. Customers rarely inform the sales clerk in a store if a desired product is out of stock,they either buy different or leave the store.