I got tickets for the Virginia game off of Ticketmaster. Normally I get tickets from a season ticket holder I know, but there has been cases over last several years where I have used Seatgeek, and Vivid Seats, for Baseball, Men’s Basketball, and Football and haven’t had any issues.
UT may not guarantee tickets purchased through a 3rd party, but SeatGeek, Vivid, and Stubhub all have their own guarantees if ticket does not work for whatever reason. Also look between all the sites as the tickets will have different processing fees. Stub hub processing fees are crazy. The other are not much better, but I have found they are cheaper on the fees.
When UT went to E-Tickets it made it a lot harder on the scalpers. You can still get tickets from scalpers, but I would make them transfer ticket from their phone to my phone before I handed over any money and do it in person if you don’t know them. Also there are still actual hard tickets still floating around, but not very many. Season ticket holders had options to be charged like $50 extra to have actual hard tickets also. But whatever you do, do not buy a ticket that’s a print out on a paper. Paper tickets will not scan from what have been told. I know the E-Tickets have a moving barcode, so a screen shot of the E-Ticket will not work either.