Noticed a weird (and kinda shady?) trend at my first Pokémon card show

I went to my first Pokémon card show as an adult this weekend and ran into something that felt… off.

Most vendors do trades at 80% of market value. Totally normal. If I bring in a $80 card, I expect them to value it at around $64 for trade.

But a few vendors were doing this instead:

• Instead of valuing my cards at 80%,
• They took the cards I wanted and multiplied those prices by 1.2.

So instead of discounting my side, they were inflating their side.
Example: If their card is worth $80, instead of valuing it at $80, they'd say it's $96 for trade because “that’s how 80% works.”

At first I thought maybe it was one vendor being sloppy, but after this happened multiple times, I started wondering whether it was intentional or just bad math. Honestly, when I tried to explain, most of them didn’t even understand what I was saying, so after a while I just walked away from the deals— even when it was only a few bucks — just on principle.

Is this a common thing at shows? Are vendors really misunderstanding the math, or is this a tactic people are using now?

Would love to hear if anyone else has seen this.