PThespian said: "Say I have a ticket that I list on three websites. Once someone buys it they want me to transfer it to them electronically.
I go into my TM account and transfer the ticket. This is the original ticket and that buyer now has it.
Someone else buys it on a second website I listed it on. I can't transfer it to them electronically because the ticket is no longer in my TM account. Those people have nothing to present to even try to get in.
Right?"
Not quite.
Typically, when you sell on StubHub and everywhere other than Ticketmaster, you are going to upload a PDF of your tickets to your buyer. On Ticketmaster, you would do nothing, since they would handle the sale and cancel your ticket entirely and reissue a new ticket (with their name, new barcodes, etc.) to the new buyer.
But there is nothing preventing you from saving off a PDF of your Ticketmaster ticket to your local system, and then being able to sell it elsewhere/multiple times, or getting in line first and having several people behind you waiting with tickets for your same seats that won't scan.
The only nuance is that if you sell the PDF of your ticket elsewhere, they are all valid tickets, but only the first person to get it scanned would get to enter the show. Whereas, if you sold it on Ticketmaster, AND sold PDFs of that original ticket elsewhere, only the person who bought the resale ticket on Ticketmaster would get in, since that new bar code was issued for that seat, and canceling out the bar code on that PDF you made before selling it.