Addition originally permitted unknown

[Doug Woodward]

We are buying a flip. The sellers bought the house 12 years ago with an existing addition.  We asked them, but they don't know if it was ever permitted.  We have two choices: 1) to rehab with all plumbing as is; 2) to increase the size of the original bathroom in the addition and to move vanity and make it a double sink.  The 2nd option would make the house show better, but without those changes there is no permitting that would be required, so no reason to invite the city in.  Have heard horror stories about having to demo an addition & that would totally blow our budget and make this deal a  non-starter.  Looking for advice on how to navigate this.