If you do this long enough, it's liable to happen every now and then. 95% of the time its the facilities error. Depending on the client, previous issues, travel, etc. I try hard to be flexible in what a fair remedy is. Sometimes I'll just adjust the invoice down to cover travel expenses (usually $25.00) and move on. If the client is a repeat offender, then I usually charge full freight.

Like cass said, its an opportunity of sorts when a schedule snafu occurs to look good.

There's a duo around these parts that's known for losing their shit when something like this happens. Safe to safe, that's never the right response.