Help Molla M with their list: Going to Ethiopia
It would be great to know what area you're talking about, Molla...but in general a tour operator or DMC should provide clear information about transfers, pricing in advance, as well as clear itineraries. Added bonuses are heading to places off the beaten track. Also, being available for questions, extra info during the trip. Hope that's helpful!
You want to focus on the operators with a focus on customer service. In Ethiopia some of the best will have a dedicated mobile number for 24/7 questions and support while travelling. Don't worry too much if they are good at web design but find the companies with lots of varied and/or complex experience. Then you know that they can handle it if anything doesn't go to plan. Great piece of mind. And of course, for the sake of the local Ehiopians pick someone based in the country and who supports sustainable tourism by contributing to the local communities they take you to.