this is why buyers get solicitors and surveyors who find out problems like this. Yur expectation of estate agents are too high. They are just sales people, how would they even know about structural problems/snagging problems. For all they know, you could be willing to buy a house with problem because you intend to pull it down and build another one. Thats none f their business, and they shouldn't have to know/ care about that. Their job is to sell the house on behalf of the vendor and its the buyers job to find out about these things.
Now that the estate agent is aware, they may tell prospective buyers if they ask but they have no oligation to volunteer the info. how would the aents rep be at risk ... if you went ahead and bought it they count it as one of their sales, and if the vendor gets fed up and puts it on with someone else, then the problem is just moved elsewhere
Bear in mind ANYBODYcan be an estate agent