IMEI Blacklisting for manufacturer factory unlocked GSM phone

Hi my cousin recently bought a phone from a classmate (she is not very saavy), she said the price was good, but after finding out more info she found out that the classmate bought the phone from a local big box store and returned an older phone back to the retailer in the new phone's box. So the older phone will likely be going back to the manufacturer, and I told her that her new phone (which is a factory unlocked GSM device) may become blacklisted when the manufacturer receives the box for the new phone and they see that the returned phone's IMEI does not match the IMEI on the box. Was I correct in what I told her? I realized afterward that most blacklists and bad ESN/IMEI's come from the carriers, so I'm not sure if manufacturers would blacklist IMEI's or if they even could possibly do that for factory unlocked GSM phones...

Aside from her returning the phone to the classmate, etc. which I advised her to do -- I'm still curious about the inquiry - thanks for any advice you can provide..

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