85% of businesses don’t take upselling opportunities and lose out on nearly 35 – 60% in additional sales revenue. Cross-selling is another factor that is easily overlooked. When this behavior changed, cross-selling amounted for another 10 – 15% of additional revenue. Up-/cross-selling is part of customer service and not a sales technique. If you don't provide this to your clients, you rob them of the opportunity to work with you or buy the right solution from you.
Upselling is when a customer asks for a specific product or service and you establish with the customer their real needs. It might happen that the customer needs additional products or services from you together with the original items they wanted to buy. An upsell enhances the original product or service that the customer wants to buy and therefore provides more benefit to the customer.
Cross-selling is once the sale and upsell are done, you simply remind your customers of other products or services that you are offering. This is a soft-sell or information-based sell and may not result in an immediate sale. This however will allow your customer to come back to you with additional inquiries in the future (some may ask immediately about it when you mention this and may even buy).
Informing people about anything else you offer (not every single product, make it interesting and use only one or two or summarize it in less than 30 seconds) is important for continuity of your business success.