You can't give an abstract riddle, like "a broken pencil and a bullet wound" because riddles should give all the information to figure it out, you just need to use your mind. You can't assume there's a hunter nearby firing bullets, or what-have-you. Most riddles have just 1 answer, and if you can come up with 50+ hypothetical answers, it's not really a riddle
My opinion.
Look, 30 bucks paid, but the price was really 25. So 5 bucks extra. He gives 3 bucks back (25+3=28) and keeps the other two (28+2=30). There's no missing dollar.