Feedback is voluntary, so neither you nor eBay can tell much by it. That is why neither the amount of feedback nor the nature of the feedback is used by eBay in determining the seller metrics eBay uses to assess seller performance.
And everyone begins with zero feedback, so to restrict sales to those with zero feedback would mean no one could ever start selling (or buying) on eBay.
It is up to people who want to collect coins (or anything else) to do enough homework and legwork to know what to buy, for how much, from which sellers. That is personal responsibility, not eBay's responsibility.
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