A pricing strategy suppliers use which sets prices primarily, but not exclusively, on the value, perceived or estimated, to the customer rather than on the cost of the product or historical prices. Value-based pricing is predicated upon an understanding of customer value. The approach is most successful when products are sold based on emotions (fashion), in niche markets, in shortages (e.g. drinks at open air festival at a hot summer day) or for indispensable add-ons (e.g. printer cartridges, headsets for cell phones).