Pretext investigations of trademark infringement usually implicate one or more of four rules of professional responsibility: truthful communications, communications with adverse parties represented by counsel, communications with parties unrepresented by counsel, and the prohibition of deceptive behavior. There is an additional rule on using paralegals or non-lawyer assistants to do the actual investigation which also comes into play on occasion.
"The Ethics of Deception: Pretext Investigations in Trademark Cases,"
Akron Intellectual Property Journal: Vol. 6
, Article 1.
Available at: https://ideaexchange.uakron.edu/akronintellectualproperty/vol6/iss1/1