If you have a soap business already, or you want to sell your products...
First of all, I've started a Yahoo Group for sellers and bath and body business hopefuls. You can read about it here. I was going to write a book or guide on it, but I thought a discussion might be better initially.
If you have a business already selling handcrafted soap or bath products:
If you don't know about this method, you must try it. It is a fast, easy way to add more profit onto your existing business. If you sell soaps, and there are a few scents that 50% of people buy (this happens a lot), come out with at least a lotion in those scents. People will buy them! They'll ask you about scrubs, roll-on perfumes, and all kinds of products in their favorite scents!
I know because this used to happen to me (I sold products for a bath and body manufacturer.) But the owners weren't smart enough to listen to their customers. They never came out with these incredibly easy products that could have kept them in business. That is one of the reasons I wrote this book - to help small businesses STAY in business.
If you want to start selling products, how hard is it?
I'm not going to lie to you - it can be quite difficult. In every craft fair, you can see at least one seller hawking their wares under a good-looking tent. If I were less honest, I would say "buy my book and you'll create products that fly off the shelves." But they don't - you have to make them fly off the shelves with sales ability.
What this method can do for you is save you time. When you own a business, you're not just a crafter anymore. You have to split your time between product development, labeling, legal stuff, customer service, selling, and crafting.
For example, let's say you want to try a masculine toiletries line with a scent of bergamot, pepper, and cypress. You probably don't want to spend hours creating the products when you just want to test it. After all, you don't even know if it will sell! With the method of customizing bases, you can whip it up in not very much time. If it flops, you're not out much time or money.
This method gives you the freedom to experiment, and the confidence that you're giving customers a professional-quality product (especially if you're a beginner.) Plenty of people use it, especially on Etsy. Plenty of people don't do it; they do everything the old-fashioned way. But I'm convinced that those are the folks that won't be able to spend enough time selling their products to stay in business.
From experience, I know that customers don't care how many hours you put into your products. They don't really care that they're "made with love" (and doesn't everyone say that?) They care about if they like the products, and if the products look attractive, feel good, and smell good, none of which requires your "slave labor." (In other words, the cliche 'work smarter, not harder' applies here.)