Most new brass cased ammo is primed with brass colored primers. Just because it has nickel primers does not necessarily mean it was previouosly reloaded. I would check the brass against others with the same headstamp. If all of the "brand X" brass has nickel primers I would be less suspicious.
Beware of Glock fired brass. It will be more swollen at the base and you cannot properly resize with conventional tools. To correct the Glock fired brass you will need a Case Pro or Magma Casemaster.
If you don't know how to tell the difference, drop me a PM.