If you've never heard of the "tourist tax" and you desire you and travel being in a long term relationship, it's time.
What is it?
the ourist tax is a common additional tax that sellers with instill to try and raise prices.
Some places simply make prices higher for buyers in more touristy parts of cities and other will try and confuse you with the local currency.
where is it?
this is common in countries where bargaining is common, places with markets and small shops.
More impoverished countries are more common from my experience,
Central America, South America, some parts of Asia.
In Nicaragua this was very common and a little bit in Mexico depending on where you were but not as much and almost never in Europe, much like the United States.
how do I avoid it?
Know the customs where you are going. There are many info graphics and articles that can help with specific towns even and what is respectful.
Don't assume that people are trying to con you but they are there trying to make money so you want to be cautious.
Ask a tour guide if it is polite to tip or if it is considered rude. Everywhere is different.