My opinion differs from Randall Wilson's. I see no practical or moral difference between knowingly overcharging someone, and attempting to steal from them. This is true regardless of the basis on which one is billing.

If my normal fee is $300 an hour but I knowingly present a bill for $600 an hour to an unsuspecting client, I'm trying to steal money. If I knowingly charge the client for services that I didn't perform, I'm trying to steal money. And if I knowingly overcharge for in-house services, photocopying, paralegals, consultations or anything else, I'm attempting to steal money.

The issue is pretty simple: was the overcharge an honest mistake, or a calculated attempt to induce the client to pay more than he should for services rendered. If the latter it's a form of stealing, just as fraud is a form of stealing.