The shop did not rip off the customer. They showed the customer exactly what was for sale, and the customer bought it. It may not be a great shop (probably isn't) but it's your responsibility as a consumer to do at least some initial research about the product/s you are interested in buying.
It sounds like the OP decided to make an impulse purchase and the shop obliged him or her.
Now, the OP understands s/he made an error in judgment by impulse buying and now wants the shop to do undo their mistake.
There's no evidence of any wrongdoing on the shop's part. If a customer wants to buy a product, any business will be happy to sell them the item.
If the shop had engaged in bait and switch, or in some other form of deception or fraud, then yes, the shop would be in the wrong. But in this case, the OP is upset that s/he got exactly what was on display. Totally different situation.
OP, sell the bike for as much as you can get on craigslist.
I think it would be hilarious if someone bought the bike, created an account and complained: I regret my craigslist purchase!