An Excel spreadsheet consultant should be proficient in advanced functions like array formulas, IFERROR, and nested IF statements. Expertise in using INDEX and MATCH for dynamic lookups, SUMPRODUCT for complex calculations, and dynamic named ranges is also essential. Mastery of Excel’s data analysis tools, such as Power Query and Power Pivot, is important for handling large datasets and performing deep analysis. Advanced functions allow consultants to provide sophisticated solutions that meet complex business requirements.