In this town, a very qualified person once started their own EC business. They were delighted to get a job for the town's largest property management firm. The first job wasn't bad, either - just replace the light fixtures in a warehouse that was between tenants.
When the inspection came, there were many unrelated items that the inspector cited. When all was said and done, the EC was stuck fixing these violations out of his own pocket. He had been suckered by the management firm.
That's the 'worst case.' Or, is it? Conceivably, should a loss (fire, injury, etc.) happen, and be caused by something you SHOULD have seen, you're likely to be required to justify your actions.
"Liability" is found, these days, in the law library under "fiction." There's precious little logic or sanity to it.
You really need to chat with a local attorney who is familiar with contractor's liability. Then, make sure to document your notification of the customer as to any hazards you may find. If the dangers are such as to pose an "imminent" danger, then you probably also have an obligation to notify the appropriate AHJ.
I have had one customer, for the past several years, whose restaurant was truly a "slice of the third world" in more ways than one. Indeed, I've posted plenty of pics here from that place. Yes, there IS a marked similarity to the pictures currently in the news, from bases in Iraq.
Yet, things have not remained idle. Steady progress has been made in correcting these faults. The owner actually is serious, and is having repairs made as the budget allows. Indeed, at one point he closed his doors for two weeks, just so the kitchen could be redone.
Not every customer is that conscientious. Keep your eyes open, and have a 'Plan B." Most of all, be willing to walk away from a bad situation.