Last night, I was quoted on the order of $800 for a domestic regional United Express flight, Y only available, one way. The same flight number, same time, same everything was for sale on my PDA tool for $370, one way. The agent suggested that they had "more real time inventory" which was why the lower fare was not available to buy from her, and suggested I just book it using the web tool, which was good advice. It ended up booking into "M". Checked today to see what the fare was and the flight must be sold out since it no longer shows up in the search tool at all. Any explanation for this? Is it possible that the inventory for sale on the web actually lags behind what is really available, resulting in this big a difference based on fare bucket availability?