We've had red bugs which are easy enough to treat but we've thankfully never had the acro eating flatworms. Like you, we now only get corals from a trusted source. That, however, doesn't mean that we don't still quarantine them to keep an eye on them for a bit before putting them into our tanks. The monti nudibranchs are a special kind of pest though. Nothing short of kryptonite seems to kill the dang eggs!