I rebooked the ticket at the same price after my call to the agent.

Upsell? Agent advised simply that is the amount his system generated. Perhaps the agent or maybe BA IT?

Many travellers would accept the agent response as accurate and pay and not re price it themselves. As far as I am concerned the BA price guarantee includes the agent call center and the website having the same pricing as it calls into question my interaction with call centers.

I have had a recent experience with an upgrade payment from WT to WT+ where different agents quoted me different prices and luckily I had an email proving the lower price from the Manchester back office.

Not huge dollars but irritating..I want to rely on what I am being told.