Whenever you walk into a store to buy fruit, or pump gasoline into your car, you can see the inspection sticker indicating that the scales were checked to see that they are giving you what you paid for.
What obligation do the communal authorities have to inspect these weights? How about other issues of business practice?
Our Gemara teaches, based on the passage in Devarim (25:14) that market inspectors are appointed to ensure the honesty of weights and measures, but no such inspectors are appointed for checking that prices are fair. Nevertheless, people from the Nasi‘s house appointed market inspectors for weights and measures as well as prices. The Gemara relates that Shmuel asked Karna to teach publicly that market inspectors are appointed only to oversee measures, but no such inspectors are appointed to regulate prices. Instead, Karna went and taught that market inspectors are appointed for both measures and prices, following the opinion of Rami bar Ḥama quoting Rabbi Yitzḥak who required price supervision because of rama’im – swindlers.
The Rashbam explains that the courts are certainly obligated to checks weights, since the customer cannot discern whether the scale is accurate. Prices, however, are meant to fluctuate on the open market. If one shopkeeper raises his prices too high, customers will shop elsewhere. Thus there is no need for market oversight.
The opinion that price controls are necessary, as well, explains that this is because of “swindlers.” According to the Ramah, this does not refer to people who raise prices too high, rather to those who sell “loss leaders” in order to bring people into their stores, where they will trick them in other ways. Others suggest that it refers to people who artificially lower prices and when their competitors have sold out they bring out their remaining stock at higher prices.