(9)While online sales of goods constitute the vast majority of cross-border sales in the Union, differences in national contract laws equally affect retailers using distance sales channels and retailers selling face-to-face and prevent them from expanding across borders. This Directive should cover all sales channels, in order to create a level playing field for all businesses selling goods to consumers. By laying down uniform rules across sales channels, this Directive should avoid any divergence that would create disproportionate burdens for the growing number of omni-channel retailers in the Union. The need for retaining consistent rules on sales and guarantees for all sales channels was confirmed in the Commission's Fitness Check on consumer and marketing law published on 29 May 2017, which also covered Directive 1999/44/EC.