Robert stood rooted to the ground as he carefully recalled what Sam said.
Indeed, Sam is a tea connoisseur. Since he said those tea leaves are authentic, it should more likely than not be the case. Otherwise, he wouldn't have offered so much money for a lousy bag of tea leaves.
If the tea leaves are authentic, the young man who gifted them to Eddie shouldn't be an ordinary person. But both Eddie and Nikki called him a good-for-nothing who freeloads off his wife, and they clearly sounded contemptuous just now. They even threw the tea leaves he gave Eddie into the trash. That just goes to show that they detest him a lot.
In that case, Sam is right. The Turners are indeed too ignorant and improvident.