A kid in the neighborhood came over on Sunday despondent because of an interaction with a card shop here in LA. I have my opinion on if the shop acted appropriately, but I'm curious what the group thinks.

Scenario
Kid (13) is looking at Pokemon singles and sees one he recognizes, and immediately gets excited because he thinks it's underpriced. Card is listed for $70 but he saw one sell for $120 earlier that week, and says something along the lines of "Wow! I saw that card sell for $120 on eBay!"

Card shop employee overhears (or was part of the convo, unsure), and immediately takes the card out of the case, checks the value and reprices it for the current comp.

Shop employee than says to the kid, "Next time you should keep that info to yourself and buy the card. You gave up your negotiating leverage." Will only sell the kid the card for the new price.

Neighbor is crushed. Learned a lesson but the hard way.

Question
Was the shopkeep right to change the price as the kid was looking to buy it, when the kid was the only reason they knew it was priced wrong? Or should they have offered it to the kid at the price they had it up for, and if he passed then list it for the larger price?