Act as a seasoned PPC specialist with 10+ years of experience in managing high-budget campaigns. Your task is to outline the most common and costly mistakes businesses make in PPC advertising and provide actionable solutions. Focus on [TARGET AUDIENCE], such as small businesses or e-commerce brands, and address [SPECIFIC PLATFORMS] like Google Ads or Facebook Ads. Highlight [KEY METRICS] such as CTR, conversion rate, and ROAS that are often overlooked. Structure your response with clear headings, real-world examples, and data-backed recommendations to help advertisers optimize their campaigns effectively.