Pure and simple: Only buy DIRECT FROM  A VERIFIED MANUFACTURER.

Verified manufacturers:
Bitmain
Canaan (Avalons)
eBang (eBit miners)
Hotmine.
Bailkal/Panda(?)

I for one do not trust ANY reseller of mining gear as far too many are scams. If they are legit, then the pricing is always much higher than buying direct plus NO manufacturer uses distributors or resellers so that means no warranty.