May I ask what your concerns are? I don't see what the problem would be; a numerical grade is not mentioned in the listing title and the coin appears to be the same. As I am sure you well know, when it comes to cracking slabs, there are plenty of sellers out there with highly questionable motives, but some collectors crack certain coins and save the inserts, so I do not see this as that unusual. Good or bad, the seller is telling potential buyers what that the coin was certified and what it graded out as, which is more respectable than those who crack dreck to sell raw while fluffing over the problems.
Sure it's allowed. It is being sold as a raw coin with no mention of a numerical grade in the title or description. The fact he has an NGC insert in the picture doesn't mean anything because it is not in a slab and there is no way to prove that insert goes with that coin. Oh you might be able to look up the coin on NGC's website and show that it is the same coin, and if you did you might have more confidence in the coin, but it is still being sold as raw. So it's fine.
