Those "serious prospective bidders" were allowed in despite Mr Murphy and his company not finding out if it was safe for them to do so, although the bidders were given a copy of the final report about the property's contamination.
One man told the tribunal he suffered temporarily from "some sort of chemical odour at the property".
Mr Murphy said he didn't know about the "drugs issue" until he received confirmation in the report.
The tribunal found Mr Murphy and his company not guilty of a misconduct charge and instead guilty of the less serious offence, having accepted they didn't know about the health risks until they received the report.
"We accept that real estate agents in such a situation are not expected to act like medical practitioners, but when a red flag would appear to a sensible person, they are expected to be open and candid and be more concerned for the health of the interested parties than to achieve a sale for their vendor client," says the tribunal's penalty decision, just made public.
The tribunal decided Mr Murphy and his company did not need any further training or education.
"We accept that the defendants did take some positive steps to ascertain if entering the property posed health risks, and they are remorseful of the circumstances we have detailed," the ruling says.
It also noted Mr Murphy's previous clean record and contribution to the industry.
Mr Murphy could not be contacted.