If you used the same text they did, they have a valid point. Have you posted your ad here, as it was listed on eBay? Did you use their pictures? If you did, being a loyal customer doesn't grant the right to use their licensed material.
With the proliferation of fraud on eBay and sales of counterfeit products, I can understand why companies would be careful about how their products are sold by third parties that aren't part of the dealer network. Easton, Look, Ritchey, and others have all seen counterfeits of their products being sold on eBay.
If they contacted you, they must have felt there was a good reason. It's likely they didn't do it just to keep the little guy down.
At any rate, there's only one side of the story here.