Rehab w/o permits from previous owner. Is this a concern?

[Rob Hallowell]

My wife and I are looking to buy our first rental property.  We found a property we like in a great location and it has been mostly renovated already. It will still need some work but we have a trusted contractor. I went to town hall to pull the files and found out the previous owner didn't obtain any building permits.  After walking through the property with a contractor the work appears to be done correctly. Is this a big concern or are we just nervous newbies?