Given a travel related situation, and given a specific question about the situation, summarize the question into a title

Example Input: The advice is given many times to not get into "illegal taxis", because they will scam you. My question is: what are the possible ways of scam, if you agree on the price and destination in advance (e.g. by showing it on a map)?

Well, I can imagine that taxi driver at the end says a higher price then agreed, but then what happens if you just give him the previously agreed price and walk away? In the answers of another related question it was mentioned that the taxi driver could deliberately "misunderstand" the location, but that would be covered by showing the map part.

For the sake of this question, let's consider only countries, where being kidnapped/robbed/killed by the taxi driver and such extreme outcomes are extremely rare. Say, Europe, US, and other countries considered "safe". (In other words, let's suppose you don't have to consider the risk that "the taxi driver will kidnap you".)

As answers I'm either expecting any theoretical possibility where you could be 
scammed, or even better concrete known instances of such scams (i.e. the tourist had to pay more, in spite of doing the above due diligence).

One particular example: I heard once (but not sure if it is true or not, since I can't find anything on Google about it), that a possible scam is agreeing on say "30 dollars" in advance. Then, at the end of the ride, it turns out that the taxist did not think about "US dollars", but "some other kind of dollars" (which of course are much more valuable then "US dollars"), and maybe he has even an accomplice to validate that ("Yes, of course, in this country we always refer to XXX dollars, not US dollars.") But as I said, I can't find anything about this, so maybe it does not exist at all.

Backstory: I was in a Balkan country, waiting for the bus to the airport, together with two locals (or at least they were from some other Balkan countries). A taxi rolled up, and offered to take the three of us to the airport for an extremely low price (basically what the bus ticket per person would have cost). I double checked the price I would have to pay with the taxi driver, before getting in, but was still expecting some bad surprise when we arrived. In the end, everything went fine though, he just asked for the price we had agreed on (and besides that I willingly gave him a tip), but at this point I'm wondering what was in it for him? (The total the three of us payed was less than half of the regular fare it would have cost to get to the airport.)
Even though I had luck this time, I still think it was foolish from me to just get into the cab, and I would like to know what else could have gone wrong. (Btw.: I used the term "illegal taxi" at the beginning, this one seemed pretty legal though - had the sign at the top, taximeter, etc.)

Example Output: Possible taxi scams if fare is agreed in advance?

Example Input: Emma Morano, who recently passed away at the ripe old age of 117 after becoming the oldest woman in the world, apparently ate a daily lunch of pasta with raw minced meat:

The Economist | Emma Morano: Ancient as the hills 

Is this an actual Italian dish, and if so, what is it called and are there restaurants that serve it to the public?   Googling in English was unhelpful.

Example Output: Eating pasta with raw minced meat in Italy

Example Input: The official UK document says: 


  You can bring in other goods worth up to £390 (or up to £270 if you arrive by private plane or boat).
  
  If a single item's worth more than your allowance you pay any duty or tax on its full value, not just the value above the allowance.


The question: 

Is the tax-free allowance applicable per an individual item or per total cost of all items combined in a baggage?

If you need a more detailed example, here it is. 

I am relocating to the UK and going to take my desktop computer with me. I want to disassemble it and put small parts into my backpack and big parts into a suitcase that will be put into aeroplane's luggage. All these parts will be with me upon my arrival to the UK.

As for the computer. I bought all its components separately in my country and put them all together and used the computer for around a year. Almost all the parts in the desktop were cheaper than the tax-free allowance except the Video Card.

What will I be charged for? For the sum of all the components prices or only for the video card? 

Example Output:
Is the tax-free allowance applicable per item or per total cost of all items combined in a baggage