You're entiled to your opinion. I have sold the sprocket already to someone else that was willing to pay $25 for it, and in fact, that person is from this site.
It's a matter of supply and demand. At some places, they'll be cheaper, some places, they'll be more money. It's a fact of life.
Do you go whining to another gas station or a store when the other is cheaper? No. It shouldn't apply different here. But then again, you're just a kid and people don't take stock in what kids say until they're 21, married, and have a family.
I am known to be generous to my buyers. The purchaser asked me if I had a biturbo, and I so happen had one, brand new, NOS... Sold it to him for $10, to thank him for his business.
So in effect, from me, for just $35, he got a speed sprocket and a bi-turbo.
If you take the time to learn what they call "politeness" and "courtesy", you can make great deals, even with those that sells things that might seem "expensive".
Reality of life: It's just a moped part that you probably wouldn't have a need for anyway. Yet, you're aggrivated. Odd how life works.