What's the most common issue you encounter when using Antminer?

My biggest headache is what if I buy an Antminer and it has a defect? That's why I've always been picking GPU over ASIC miners because I know that when I buy from Nvidia or AMD, it's gonna be a high-quality product, while I don't have the same sense for Bitmain. The problem is that if the miner that I bought from China has a defect and I have to return it back, I'll have to pay hundreds of dollars for shipping from my country to China, which isn't worth it for me. Buying from a local market is a bad idea because they sell antminers at double the price.
You mentioned the most basic rule for a miner. You don't need to buy something that you can't repair in your country.
First, you need to find a good service and find out the repair prices to calculate the risks. I know that
official service centers have their own rules: if 4-5 chips burn out on the board, they change them; if more, the equipment can be sent to China, and that takes a very long time.