What are the differences between 3g modems (industrial and usb)?

Question

Telephony

I select a modem for a vending machine. With an eye to the possibility of manufacturing devices for sale in the future.
Conditionally, I divided the found modems into 3 categories:

• USB modems. From the cheapest for ~500r to 2-4t.r
  
• "Modules". Most came across PCI, there are others. from 2t.r to 8t.r
  
• "Industrial modems". Raznih shapes and sizes, from 2t.r to infinity.
  

Help me to understand:

1. What does "industrial", a beautiful word? Maybe somewhere it is impossible to use NOT industrial ones?
   
2. Why are "modules" so expensive?
   
3. Are there any restrictions on the use of usb modems (for example, purchased from an operator) for commercial purposes? As an integral part for the production of other equipment?
   
4. Probably the cheapest models from aliexpress do not have IMEI, the necessary certificates. Can they be legally imported, sold, used?
   

Please correct me if the questions are not worded correctly. Clarifications are welcome)
Thank you!

Answer 1

In the original sense, "industrial" is usually for a wider range of operating temperatures, humidity and power. Well, as a rule, it is really designed for long-term trouble-free operation.
Household usb whistles sometimes hang merrily and they need to a) provide for the circuits for manipulating their power b) provide for the implementation of distinct mechanisms for juggling the power
Well, yes - if the production of vending machines implies industry - then one way or another, the question of guaranteed reliability of each node will not be at the level "mom swear works like clockwork")