One common mistake when selling items on Etsy is having poor product photos. Make sure your photos are high-quality (well-lit) and show your items from different angles. Another mistake is not having a clear and concise product description. Be sure to include all relevant information, such as materials used and item dimensions. Lastly, don't overlook the importance of customer service! Respond promptly to questions and concerns, and ship items in a timely manner to keep your customers happy.