A busy till tells you that customers are buying. It does not tell you how much the business keeps. Start by separating revenue from the costs required to earn it: stock, packaging, delivery, transaction charges and overheads.
Look at one product or service at a time. Subtract its direct costs from its selling price, then consider whether that contribution covers the business’s regular expenses. A product can sell quickly and still contribute too little.
Review discounts, waste and unpaid invoices alongside sales. Track costs consistently before changing your prices, and use the same period when comparing sales and expenses. Better visibility makes it easier to decide which sales are actually worth growing.