Is the panel surface or flush mounted? Surface mounted will be easy, flush mounted, not so much to do it the right way. They might be appeased if you can find a snap in bushing the correct size, cut it so it slips over the bundle of wires and snap it in. It's not up to snuff as far as the code goes, but it's a helluva lot better than the cables resting on the edge of the hole.
I've pissed off enough realtors that I rarely do many home inspection lists. By the time I would get involved, the inspector had made his report and gave his recommendation, the buyers made the request, and the seller had signed off that the repairs would be made. From what I understand, if the repairs aren't made, the buyer can back out of the sale.
There have been a few that I wouldn't do because things that the inspector missed weren't on the list would have to be addressed and of course, nobody was willing to pay so I walked.