Teenager charging $300 for art?!

I've been trying to decorate my new baby's room. I've found some art pieces but they're all so expensive. My cousin said she has found some art on Facebook Marketplace so I looked and saw someone selling some paintings. They were being sold by the same person. He was selling them between 300 and 500 dollars! I went on his profile and he said he goes to the local high school and is clearly a teenager so I messaged him to try to negotiate. It was $300. I said I would give him $50 at the most. He said no thank you. I told him that's okay. Just know he will have a hard time finding someone to pay for that much for his and he said "Actually, I've had 4 people buy my paintings. Someone bought one for $600. Thanks but some people see the value. Good day!" I rated him one star because he was rude.

I found out that I'm in a mom group with his mother and posted a screenshot of my profile saying how I tried to low ball her son and that I have a habit of leaving fake reviews. They're not fake. I rated them one star because they're rude and don't even try to negotiate. I live in a small town and feel like everyone is all ganging up on me. I'm not sure what to do.