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You need to raise your prices by 10% to 20% once or twice a year. This is very important. Everything goes up in price over time; therefore, your work needs to go up in price as well. Most artists price their work way too low and rarely raise their prices. In fact, many artists price their work at wholesale prices in a retail situation, which means they could double their prices overnight and be priced just right. The same artists keep their prices the same year after year, even though their own expenses increase regularly. As a result, their income decreases further and further. When they finally realize that they need to increase their prices it is often too late to implement just a small increase. Instead, they have to double their prices (or more) overnight, and the result is that most of their customers can no longer afford their work. This is a situation that you want to avoid. Therefore, I recommend that you raise your prices slightly, by 10% to 20% once or twice a year, depending on the economy and on how comfortable you feel regarding your sales.
By using this approach your prices will increase regularly without this increase being noticeable. Nobody will object to a 10% to 20% increase. In fact, most people will not even notice. But everyone will notice if you double your prices overnight.