When you are selling products across multiple channels you should aim to keep a consistent corporate brand across all ecommerce channels to instill maximum customer confidence. Brand recognition is one of the keys to success, as people will relate your logo design and colour scheme to your quality products and services.
If your ecommerce design, eBay store and Amazon shop all use different styles of logo, colour scheme or brand identity, your company will simply look unprofessional. Keeping consistency across all areas will ensure your company reflects its high quality products and services, and will ensure customers have a high level of confidence in you to part with their well-earned money.