I purchased tickets for the Bears and Lions games before the season started through the Rams official Ticketmaster links on the website. Never was I asked if I was a Rams fan or not. I went to the opener but ended up getting really sick in October and couldn't attend the Detroit game.
Right there on your Ticketmaster dashboard is the ability to sell the tickets you bought. You can set your own price. They don't ask which set of fans you want to sell them to. It will notify you when someone has bought your tickets and you'll have the money transferred directly back into whatever payment method you used after the game has been played. I checked the seating chart after I listed them and there they were at the price I set ready for anyone to buy.
I was shocked it was so easy. I'm sure people are just buying up tickets on different accounts and reselling them for profit.