Wait, the gate agents offered you a voucher but later said they didn't? Were these the same agents?

I had my first DL flight in years today (status-matched refugee from AA), flying PDX-ATL-LGA. Offered to bid on VDB on kiosk, and I bid $300 (lowest offered was $200). At the gate they were offering $500, and I took it. When he took my BP I just asked "$500, right?" to clarify, and that's what I got.