I don't know if I would characterize them as having monopoly control of the market because nearly 100% of all of my purchases are made online and 0.0% of my purchases have been made using amazon.com (or walmart.com).

Generally speaking I prefer to buy a product directly, or from a specialized retailer.

Last week I purchased a stethoscope from an online stethoscope retailer. A benefit of doing this is that they offer laser engraving-- something that Amazon, with its warehouses of robots and robot-like employees, cannot easily do.

The specialty retailer also carries a wider array of color and finish combinations, because that's their product niche.

Using a specialist retailer has allowed me to flex on my fellow volunteer EMTs with a personalized Technicolor stethoscope, which is dumb but nice.