An industry with N firms has successfully lobbied for protective regulations.
Regulations require all firms to charge a price p that is greater than the marginal cost c.
The firms were unable, however, to also get the government to ban advertising. As a result, the firms are tempted to use advertising to gain market share. Pick two very well-defined products that you could buy on an online auction site, e.g. a 1989 Upper Deck complete factory sealed set of baseball cards. Look for the products on Ebay and on Yahoo Auctions. Estimate the number of times the product is available for purchase in a month, the fraction of the listings that result in sales, and the average selling price conditional on a sale occurring.