can they mark this iphone as stolen and ill be out of my money?

so i bought an iPhone 5 from ebay i like it its nice an clean. how ever when i tried to register the device under my appleid. it said i cant due to being register under other apple id. no big deal right i contacted the ebay seller who happens to be a pawn shop owner told me that he has no idea who the original owner of the phone was there for no way of knowing who's id the phone is register to. i have the phone now i got service with att clean imei. my problem is who ever the original owner is could he just call in apple and give them the the serial number and say it was stolen? even though i bought through ebay and has new service and all