In addition to depicting the underground market for firearms, this clip is also useful to spark a discussion about gun control policies. Walter could purchase a gun legally since he doesn’t have a criminal record, but he’s willing to purchase an illegal one without a serial number.
The price system motivates Gus to purchase the equipment for the chemistry lab, hire the resources needed and take the risk to produce and distribute the methamphetamine. Gale is shocked by the investment, but profit motives are often used as the incentive for investments. Firms only invest in resources if they believe they can lower the cost of production (given a fixed output) or to increase production either of which would increase profits.
In a small Mexican town, some of the locals do not walk but crawl towards the shrine of Santa Muerte. This behavior is a perfect example of how cultural norms create markets, in this case for knee and elbow guards. There is no government authority dictating that people buy the guards or that people sell them, but it happens organically. What other items do you think would be popularly sold along this passageway?