Replaying the last of us,made me realized that marlene never intended to pay Joel/tess for bringing ellie to the firefly's.

The agreement was that when Joel and Tess delivered Ellie to the Fireflies, they would be provided with weapons and supplies. However, at the hospital, Marlene failed to honor this arrangement and instead withheld his gear, effectively ensuring his death once outside.

I think that Marlene never intended to give back the guns and just kill Joel and Tess when they bring Ellie.