Most of today's miners usually buy and sell ASIC miners through Ebay and Amazon. In the e-commerce market, these are the 2 largest e-commerce sites in the world, but the prices are very high.
Alternatively, you can also order an ASIC miner at the Bitmain homepage. The types of coin miners here are sold at a much cheaper price.
Despite being the 2 largest e-commerce sites, I still wouldn't trust the ASICs sold in them, just like those sold in Alibaba/AliExpress. They could be faulty or not what you expect.
In most official sites like Bitmain, the miners are already sold out.
Not only faulty or at a minimum well used, but it is also much too common to find that they they are infected with malware that will try to spread to all miners connected to your network.
If you buy any miner through a seller on Ebay, Amazon et al always:
1. First download the latest firmware directly from Bitmain, Canaan or whoever made the miner onto a laptop or other PC that can later be isolated from your network and the internet. After getting the firmware, disconnect the laptop/PC from your network and using either a hub or crossover cable connect it to the miner.
2. Follow instructions on how to flash the new firmware onto the miner. This
should remove any chance of malware.
3. Input your pool and workername settings, save & apply. When the miner reboots, make sure the pool and worker information is the same as you put in.
4. Only after all of that should you put the miner onto your network and have it access the internet to start mining.
