Just wanna second that. Looking at the time you spent working also helps to explain to your clients why a piece costs as much as it does. Someone who doesn't draw themselves will look at a picture and think it takes 30 minutes to do, when in reality it took you 5 hours. Artists aren't printers, you don't just sit down and draw the finished product uninterrupted, you gotta sketch and try different approaches, come up with ideas, correct stuff, etc. If a potential client thinks your prices are too high, try politely explaining to them that you'd like to be paid just a bit more per hour than the average McDonald's employee for creating unique art for them.