I flew MSP-JFK yesterday on the 3pm flight. I checked with the SkyClub around 1 pm and was told the flight was still positive space but when I showed up at the gate about 45 minutes before departure they were looking for one volunteer with protection on a later LGA flight or a JFK flight the next morning. The first offer was $500 and I let them know I was open but I was on a paid F ticket so needed the same. Even though I could find flights on the app with bookable F, they weren't willing to work with me. So be it; their offers went to $600 and then $700 with no takers. I boarded (needed to grab the overheads as I was in 1A) and told them I would take $1,000 and accept a downgrade to Y if they still needed me but they didn't. There were at least 8-10 uniformed Delta pilots and flight attendants on my flight so I suspect the oversell happened due to the need to accommodate commuting staff.