Ticket scalpers (in person) have always been viewed in a negative light and carry a bad connotation. They are known for manipulating the market to turn a profit.
Online ticket flippers on the other hand have not had any negative judgement because they are simply never seen by the public.
So what are the moral implications of the ticket resale market?
You essentially would be using the mismatch of supply and demand in the market to turn a profit. The profit that you make comes from the consumer, the one going to the event. Making money selling tickets essentially makes the event goer pay a higher price for the entertainment.
When a show sells out, the venue has already made their money. By flipping the tickets afterward, the actual venue is not suffering any losses (other than the naturally high price of tickets)
At the same time, event goers that buy your tickets did not plan ahead at all for the shows, they are purchasing them at the last minute (They are sold out of course!). It is arguable that because the ticket resellers have the capital to plan ahead then it is completely fine.
You can read more about this here: https://en.wikipedia.org/wiki/Ticket_resale
The capitalistic system essentially allows for this to happen. But it is really up to you about what you think about the ticket resale game. What do you think of the morals of how to make money selling tickets?