What cultural faux pas should I try to avoid making in Burgas?

"It is important to be mindful of cultural differences when visiting Burgas. It is considered rude to be late for appointments or social engagements, so it is important to be punctual. It is also important to dress modestly and to avoid public displays of affection. It is also important to be respectful of religious customs and to avoid discussing sensitive topics such as politics. Additionally, it is important to be aware of the local customs when it comes to tipping, as it is not customary to tip in Bulgaria," remarked another expat in Burgas, Bulgaria.