project fi phone - meaning of sprint poc & fed and future problems

[deepasadish]

Bought a used phone. This is a phone that was used with project fi.

ESN check passes tmobile/att/verizon and NCIC.

For sprint it fails with poc:false and fed:true.

What does this mean:
1. Is the device fully paid for? I guess yes.
2. Is the device tied with another account? I guess yes.
For #2, what does tied with another account mean? Can I get it removed? I can't contact the seller. Tried but no use.

3. If I use it with tmobile (say), can sprint blacklist the device in the future causing me problems?

Thanks.