I am a strong believe of focused marketing. Amazon sold books in the early days as you know, and they were amongst the first of not the first to sell books online. They identify themselves as the platform to sell BOOKS. Once they have a massive double market place and became successful at selling books, they then reach out to other sellers. I remember in the early days I was not interexted in buying books on Amazon, but I did know about them. Once they added DVDs to their platform, I was hooked. Start centric with a focus demographic or an area of the market you can dominate, and then expand out to the next set of products by perhaps surveying your existing database of customers. "Hi Mr Customers, we noticed you have been buying books from us for awhile now, if we start selling DVDs on our platform, would you buy it?". Don't be afraid to ask your customers for quick survey. Perhaps offer them a $20 coupon towards their first purchase of the new line of product you plan to sell after plants.