Widgets, Upgrade Elites if they want to be upgraded, absolutely. All elites are entitled to C+ free on day of flight and I'd even upgrade 1 companion on the same PNR.

Upgrade regular pax who don't wish to pay? Would you upgrade that pax to F because they bullied you? No different.

On a similar basis, I watched and listened when the Sky Club admission rules changed (and still see this happening) and AMEX Platinum cardholders were told that they had to pay $29 for a second person. The SC Agents got a lot of grief and some abuse but quietly explained that these were the rules and that there were no exceptions.

You just need to develop a brief explanation and stick to it. If you're not a Delta Elite and you want to sit in C+, you must pay for it.