The one best thing you can do in having a city guide is to ask the locals around. There are many things which are never written or told to you by your traditional guides like the best food available and the short cuts. This is only possible if you get good interaction with the locals and try to ask them where to go for goof food or bar. This is very important if you want to know the place inside out. This is really easy for the people who know the native language otherwise mostly people know English and you can easily communicate to them in this language.