Basketball Tickets and Sports Cards

Hello,

 

I resell some of my professional basketball tickets I own and already have the 1099K details.   Additionally I sell online collectible cards.   For each, am I reporting on the net sales or income?

 

Example:  Cost of the tickets for a game are $200 a seat and I sell for $400 a seat.  Gross sales were $800, but income was $400.  What am I being taxed on?