how to check ? may be we can learn something here.

Unlike iphones sold in US, all iphones sold in MY from telcos are sim-unlocked. what we worry is imei locked by telco if original buyer doesn't comply with contract
AFAIK, just get the seller to provide initial purchase receipt, some honest sellers will declare their telco set & a few won't.
also some seller will declare their sets are gift from company/individu. just ask them to proof.