Some cleaners are pretty specific on what they will take off. My guess is if you're getting smudging then there is an oily texture to the dirt. Make sure you are using quality products and follow instructions and there is no reason you can't do as well as some shop. There's no magic. They all had to learn too. A benefit to sending to the manufacturer is they will not only clean the sensor but also give it an inspection. Oil has been an ongoing intermittent problem they may correct for you. Choice is yours.