Welcome to the Community, ayushi. I can help share some insights regarding the difference between these two reports.
Income by Customer Summary report is your income less your expenses for each customer. This report shows your gross profit from each customer.
Sales by Customer Summary report gives you the total sales for each customer.
If you need more help running basic financial reports in Quickbooks Online, please check run reports in QuickBooks Online. This gives you a snapshot of your business.
Feel free to visit again here if you have any additional questions concerning reports. I'll be glad to help.
