Tipping can be an awkward and uncomfortable situation for many people. How much is too little versus how much is too much? Is it customary to tip your garbage worker and you mailman? What about the guitar playing songstress at your local coffee shop? Luckily there are rules of thumb for the myriad of service industry professionals that rely on tips to get by. We spoke to Coupon Sherpa writer Kate Forgach, who spilled the beans on whom to tip, how much to leave, and what the unspoken rules are of tipping.