Until people pay you, all you have is a list of assumptions. Market research, surveys, and feedback from friends and family can point you in the right direction, but the calling card of real product validation is the sound of the cash register ringing. So, the first and arguably best way to validate your product is to make a few initial sales.

There are, however, a number of ways to validate your would-be idea as you're developing it. Most focus on a single essential action: commitment. Let early customers commit in some form or fashion to show that, yes, people really are interested in buying this product and they aren't just telling you what you want to hear.

This bias toward speed and experimentation can save you from costly mistakes down the line. It's advice so simple and obvious it too often gets dismissed: make sure you're selling something people want. Here are a few ways to test the waters before diving in.

Set up a store to take pre-orders. Imagine having product validation before developing your product. Pre-orders make it possible. Over the years, customers have become more accustomed to and comfortable with paying for a product today that they'll receive later. Describe and sell what you're building, honor your promises, and cast your net before placing that initial inventory order.

Launch a crowdfunding campaign. Kickstarters aren't the cure-all tonic to your financing woes, but they are still an advantageous way to get funding from the best possible source: customers. Kickstarter isn't the only game in town, either, which is helpful for brands working outside of the platform's most prominent product categories.

Sell products in person. For certain products, like homemade goods, local fairs and markets offer the ideal way to test a product: by creating an initial batch and selling to customers in person. When Nimi Kular and her family's business, Jaswant's Kitchen, first started selling their homemade recipes, they found this approach indispensable. "Selling in person at a craft show or local pop-up is a great way to share your story, get feedback, and explain the benefits of your product to potential customers," says Nimi.

There are other ways to validate your product ideas, but when in doubt, start selling as quickly as possible. There are downsides to moving too fast—if you rush and try to sell a product before it's ready, all you'll learn is that people don't like bad products. But, our experience is that most entrepreneurs wait too long to start validating their ideas.

Consider this: if you're customer-driven, then trust your potential customers to guide you to the right product. No matter how clever you are, there's no substitute for direct, pointed feedback from a paying customer.