Many retailers leave money on the table because they don't complete the sale. Their customer makes the initial purchase of a particular product but the sales associate does not ask them if they want additional items that are related to the initial purchase. Here are just a few examples:
Eyewear: protective cases, cleaner
Electronics: batteries, power bars, extended warranties, high quality connecting cables, cleaning products, bags, etc.
Pets: food, treats, cleaning supplies, deodorizers, shampoo, etc.
Furniture: lamps, pictures or paintings, coffee and end tables, throw cushions, extended warranties, fabric protection
Footwear: cleaners, polish, shoes trees, arch supports, insoles, conditioner, extra laces
Appliances: cleaners, polish, extended warranties, baking sheets/pans, etc.
Patio Furniture: accents, umbrellas, plants, wall hangings, candle, bug repellent, etc.
The list could go on but hopefully you get the idea.
The biggest challenge is that front-line sales associates feel they are going to be perceived as being pushy if they suggest additional items. However, let's look at it from a customer's perspective.
When I bought my first computer many years ago the sales associate did not suggest a power bar or extension cord. When I setp up the computer I discovered I needed these because I did not have enough receptacles close to where the computer was located. Do your customer and yourself a favour: suggest additional items and complete the sale.