[em-bee]

Married couple will have higher documented income, while unmarried cohabiting couple won't

that seems to be the problem then. i think generally, hiding the income of a divorced partner is difficult so making your first scenario less likely in many places.

and the other case would also require one partner to maintain credible evidence that they actually live apart and do not support each other. where i come from this is not easy to do.

if you live in an area where this is possible then that's a disappointing state of local legislation.

either way i doubt there is a large number of people doing this. at least i hope not. and it may as well be considered fraud.

i wouldn't bother reporting it though, because it is not going to improve your own life.