Hey there :) This is not a phrase in English, so there's no correct answer. I've never heard this phrase before in my life. Sell, as you probably know, means to offer something for money, it also can mean 'make it sound good' in some contexts. Infection usually refers to a bacteria or virus. If you get an infection that means that a harmful virus or bacteria has entered your body and made you sick. So, you understand the words themselves. Because it's poetry (well, a song) it will have a different meaning to different people. What do you think it means to you?