Sign Confusion: "Feed the Horses, $1.00"

It's a beautiful summer day, and as I walked out of the restaurant, I glanced at the carriages lined up to give tourists horse drawn tours of the area. It's a nice thing, and I'm glad they're there. I like to see people enjoy the rides, and I admire the animals.
   For the first time, I noticed they had a basket of paper bags of feed, and a sign that said, "Feed The Horses. $1.00"

   I thought I would save the young driver some work. So I said, "I'll feed your horse for a dollar."

   He thanked me and handed me a bag of feed.

   "Where's my dollar?" I asked.

   "Excuse me, sir?"

   "I prefer to be paid in advance, but only because we just met."

   He looked perplexed for a minute. Then he said, "Sir, you pay me a dollar."

   "Why would I do that? This is your horse, isn't it?"

   "Well..." He thought for a second. "Yes, but the feed costs money."

   "The horse is going to eat with, or without me, isn't it?"

   "Of course."

   "Then why would I pay you a dollar to use your feed to feed your horse. I'm doing you a favor by feeding the horse so you can stand there and relax." I smiled. "I know you probably get paid more than a dollar to feed and care for the horse, but don't worry. I don't mind doing this part of your job for only a dollar. You seem like a hard-working young man, and you should get the profit from my work."

...Strangely, he decided he didn't need my help.*

*This conversation took play only in my head, not in real life. The imaginary conversation was enough. I paid myself a dollar for giving me something to laugh about as I walked to my car.