I see both sides of the situation . Sadly, it sucks on both ends.
Often sellers try to maintain a good reputation, so they will take refunds. However,this doesn't seem to be his prerogative in your case.
That being said, you did buy it and I assume inspect it. You had some responsibility in the interaction as well. Anything I buy over 100 dollars these days, I use a Loupe after dealing with a similar issue in the past.
@The Lions Den Gave me good advice on how to use the Loupe ... it's all about the dots