Dan, was the card seriously under-graded?
Did you publish your phone number and demand him to call you and or ask him if he has ever owned a jock?
Did you lowball him on the item and then when it didn’t work out come on a public chat board and slam his cards as over-graded garbage?
Did you explain that you’re most likely one of the top 5 T206 collectors of Net54?
If not those are options that you can try as well in the future vs. calling him an idiot.