Someone called me a scammer

Someone called me a scammer for trying to trade a shiny shark for 4x under rap. Rap is listed as 4 billion + and I was trying to trade it for 2 pets that combined for just barely over 1 billion.

Now I know people say rap is not the real value, but how are you supposed to know what is? I know you should shop around and look at what others are selling for but with it being a shiny there’s no way to search it specifically. And there were others in the same server we were in selling it for rap.

This is the second time I’ve gotten a pet that people say aren’t worth rap. I’m just curious how everyone else seems to know this. Is there a memo I missed or something? Is there a list or video online that tells you to steer clear of certain pets/items?