"Pay close attention to a seller's feedback and reputation""
Yep..this is what you want to look for: good, and plenty of, feedback.
My hubby is a numismatist who buys and sells coins worldwide on ebay. He rarely runs into any difficulty using ebay/paypal. They have good customer service, both from the buyer and seller point of view.
My hubby has over 7000 positives. No negatives or neutrals. This morning he told me of a dime he purchased for 8$, resold last night for 78$. That sort of thing keeps our puppies in kibble.