I think one of the things that the real estate agents are concerned about is that if someone has a house that tests high, then no one is going to want to purchase that house. But the evidence in the States where there are requirements for disclosure has been that people actually prefer a house that's already been fixed. With the corollary of asbestos, if you bought a house that had asbestos but has now been remediated, you're going to feel much better about being in that house than having to start from the beginning and testing it yourself.
It doesn't appear to be a stigma, at least in the United States, where people are required to disclose whether or not a house has been tested.