One vital component of an offer is the investigation period, which most buyers know is their opportunity to do any necessary inspections. And it's highly recommended that they do, in fact, take full advantage of this opportunity by bringing in competent professionals to be as thorough as possible.
One additional due diligence task is verifying that improvements a seller has made have the appropriate permits. Typically, any new electrical, plumbing, addition of walls, etc. requires them. No need to fret though if the seller didn’t pull permits as it MAY be a relatively easy fix (depending on the scale) with an after-the-fact permit.
The key here, however, is to require that the SELLER do this, which means the request needs to be made DURING your investigation period. And just the request alone won't suffice, it needs to be agreed to by the seller. By doing this, the responsiblity of ensuring that the proper permits are issued falls on the seller.
Hope this helps as I feel like it's an often overlooked step that can create some major headaches when you sell the home down the road!