Gift Basket Companies

How do gift basket companies work? Say you get majority if not all of your products from a certain company, why would they sell to you when they could do it themselves? It's really just assembling the various goods into a new package. Is this a viable business? Could I just buy wholesale from them and do my thing? How and where does liability fall?
Sorry for the rapid-fire questions, but they've been on my mind and I've yet to find answers.