Sometimes a customer will try to offer a tip, often from the US where these things are much more a part of every day life; I usually encourage them to place it into our charity bag as we can all feel good about that. In the old days we regularly would be bought perfume by the First class pax particularly from the Gulf states (the Bar operator would tour the aircraft with a pad noting down what everyone wanted) but its been many years since that was acceptable. The only time you get a tip in the rear cabins it is usually accompanied by a phone number or business card
As to which is cabin is preferred, it depends on the individual. Some like the attention to detail required at the front and some prefer to have a laugh with the folk at the back; the middle is often less popular for some reason. There is no pay differential for the different cabins where I work although you need some seniority to be trained to work in First.