Recently I bought a bv7000 in an Aliexpress.
I checked the serial number of the device in the system, and there is no unique code, just an alphabet is written.
Question to the admin (maybe to people who know) - is this normal for bv7000 or have I sold a fake smartphone?
Require a refund to Aliexpress?

That is normal for this device. We identify the BV7000 devices only by IMEI number. I think you received an original phone.