Upselling, additional sales and cross sales

These are not the same even though they are often mixed up in daily conversation on the management level i companies. 

• Upselling is selling the same card but with a bigger engine
• Additional sales is selling 3 for the price of two or selling extra tires to the car.
• Cross sales is selling a bottle of water or candy bar in the pet store

Do all three and you will gain success.