While it's important to ask the contractor about any permits needed, don't think that due diligence after that isn't required. Many cities and counties have online resources that will let the homeowner know what is required from renovation or construction projects. Use those materials to double check your contractor, or call the permit center and inquire about any necessary codes to follow.
Another important reason to double check permits with the city or county is that your homeowner's insurance isn't a fan of unpermitted work; if something does go wrong, the chances that they'll cover your claim if the correct permits haven't been pulled is very slim. You can even go the extra step and check with your insurance about what permits are required, should a claim be filed.
If you're still yearning to build a stronger base of knowledge about contractors or home improvement projects, read on for lots more information.