Right you are! Always quarantine from anywhere, as you could be introducing parasites unfamiliar to your pond.
The eBay sellers that caused the trouble sold fish that either a) clearly manifested disease or b) carried genetic abnormalities that caused them to die within weeks or months. If a breeder's fish die, they should stand behind them and give refunds, not disappear or change the business name.
Anyone can make a mistake. Selling live animals is risky business, and eBay won't even allow mammals on their site as a result. A merchant's reputation rests on "making it right." A local dealer will be hammered by negative word of mouth and will be inclined to satisfy you face to face if a problem arises. If dealing locally is not practical, finding a dealer like Steve Hopkins with lots of satisfied customers and a sterling reputation makes all the difference.
BTW, your eBay goldies are beautiful! If you have good luck with them, be sure to spread the good word about the seller.