There is nothing guaranteed in electronics, my Pioneer grey market one works fine for 4 yrs now but my friends went kaput in 3 months, another one bought with bill and his Pio died in 13th month so no warranty.
It also boils down to your luck. But all said and done, in today CD player maturity, I wouldnt really bothered and will take the risk in HU. But be ready for the consequence of the following:
1. Without bill, u cant be sure of originality
2. Possible used product being sold with the panel alone changed
3. possibility of internal components being altered or selling a returned product
End of the day, its u r call mate and u r risk for appetite, there is not yes or no to this.