Ethiopia is a country very familiar with foreigners, and tourists, therefore many here are well adapted to people not knowing much about what is going on when visiting from another place.Some people have developed special protocols and means of dealing with people from other countries that everyone should be aware of. These means of being aware are somewhat different and similar, depending where you go in Ethiopia.
In general, you should always find out the price from someone on the street before you go to purchase something. If you are taking a Bajaj or a Minibus Taxi, ask the people sitting next to you what the price is before you pay the conductor. Check around before you make a purchase, you may find a much better price.
And most importantly: never leave your belongings in an unsecured area. If you stick to these simple words, you'll surely encounter much fewer issues than the vast majority.