Would that the client knew this too.
Ever get into a discussion about a project with a client only to find out that someone told them it should be easier, simpler, faster or cheaper than you just stated?
Somewhere between your thinking and their reality is what you are looking for, in both time and money. Don’t leave money on the table, but don’t lie to your client either. If you use their time and their words, you can not go far off course. But taking advantage of someone who does not know the difference may come back to haunt you next time you try to do business with them. Don’t be short sighted.
Theory works very well until someone needs to get work done. Then what should take a minute takes 15 or 15 hours. Sometimes, that is how it happens. Other times it really does take a minute. Be open and upfront with your clients and vendors, and they will be with you too.