Lima is a huge city (about 7 million people) where the vast majority do not own a car, and public transportation expenses take up a significant chunk of their income. In contrast, almost everyone in the U.S. has a car and the expense associated with it is usually a minor part of personal income. In the U.S., businesses tend to be situated at a distance from other business that sell similar products (with a few exceptions, like restaurants). Here the businesses of one type tend to aggregate in the same area, because people are more likely to shop in an area where they can find lots of choices without spending extra time and money on transportation. When I recently went to shop for furniture, I found dozens of little furniture stores within a couple blocks of each other.
The huge majority of businesses in Peru are very small operations with just a few employees. They operate with very little capital, and their collection of merchandise may have a theme (like cleaning products or kitchen utensils), or it may just be a random collection of things that the owner thought he could sell at a profit. If one business seems to be having a lot of success with a particular item, others nearby may start selling it even if it has nothing to do with the other products that are being offered. For example, here´s a baby products store on a busy street.
In the same block, there is also a bicycle store, a furniture store and a mattress store. All three of them are now selling baby strollers in addition to the products that you would normally expect to find in their stores.
Unfortunately, some of the areas that offer the best selection of certain products are relatively unsafe. I recently went to buy a recycled stainless steel cylinder to build a stove, and was glad to have two friends with me because it didn´t look like a place where I would want to walk alone.
There are lots of ambulatory vendors in Lima who sell products or services. The knife sharpeners are my favorite. They pull a small apparatus that sits on top of a bicycle wheel, and when they stop in front of a home or restaurant to sharpen their knives, the bicycle wheel is operated to power their grinding wheel. They each have a high-pitched flute which they play to announce their presence in a neighborhood, so you always know when they´re passing by. I don´t know how they all ended up adopting the same ¨trademark¨ in a city so huge, but I´ve heard their flutes in lots of different parts of Lima, so I´m convinced that they all use them. Similarly, the trash collectors always bank on the side of their garbage truck with a hollow metal pipe when they come down the street.