Always act professionally in dealing with everyone involved with the project, even people just visiting or on site.
Many people on construction sites may act in what is often expected as typical behaviour (language, personal habits, criticism of others).
As the project manager it is important to not join in with that, but to act professionally.
This can give the client, visitors, or other stakeholders a good impression and better confidence in your work.
Particularly don’t criticise anyone in public. Besides making that person angry or embarrassed, it could be heard by clients and assumed to mean there are problems with the project. Keep all criticisms private (between you and the person).
Refrain from criticising third persons, as the person you are talking with will come to know you as a criticiser.
Professional behaviour increase client confidence and can lead to other contracts with them or with other witnesses.