I work for an electronic device ODM/OEM maker in Shenzhen. In the business sector, but was once heavily involved in R&D.
It is true that you can walk into a shop and get electronic parts. It is also true that you can get PCBs in a shop, but probably pre-made ones.
For serious business, you probably want to ask for samples from serious suppliers. But usually, you will get the parts you asked for on the second day, or within a week or two for a simpler PCB.
It used to be "walking distance" for all electronic components, maybe 10-20 years ago, but since the cost of living has increased in Shenzhen, factories are moving away from the center of the city. But still, if you really want something today, within a 1-hour drive, you can get what you need.
It is true that you can walk into a shop and get electronic parts. It is also true that you can get PCBs in a shop, but probably pre-made ones.
For serious business, you probably want to ask for samples from serious suppliers. But usually, you will get the parts you asked for on the second day, or within a week or two for a simpler PCB.
It used to be "walking distance" for all electronic components, maybe 10-20 years ago, but since the cost of living has increased in Shenzhen, factories are moving away from the center of the city. But still, if you really want something today, within a 1-hour drive, you can get what you need.