Music is used in TV commercials because a song is more likely to get "stuck" in your head than just someone talking about a product. Then, when you see that product online or in a store, you will have a higher chance of buying it if you have a connection with it (remembering the song). It is a marketing technique.
Accidentals usually apply to all repetitions within the measure in which they appear, unless canceled by another accidental sign, or tied into the following measure.
