Buying a blacklisted iphone att ebay or person?

I qant to buy a iphone 5 att and unlockb it so i use on tmobile but I heard so much about iphones being blacklisted and getting it and having to go through a lot to settle it I want to know if I can unl ock it it if its blacklisted? Or if thats the case can't the person just get one and unlock it before it get reported? And its good or is it still bad? So what i'm asking is if I do get one do I hurry abd unlcok it so i want get in trouble? Or can I just unlock blacklisted or not and have a nice clean unlockrd iphone 5

I'm in the same situation, i bought my iphone 5 of craigslist and it was black listed now i'm suck with an iphone 5 that doesn't work.