The secret to a successful startup..? Sales. Without them no validation, no feedback, no customers, no business!
Follow the Lean Startup approach and do a controlled release of your product or service to some people (or businesses) you think would be interested.
By recording their feedback you will eliminate expensive future mistakes, discover that you were wrong and there is no market or receive a couple of orders which will allow you to beta test.
Another option is to contact one of the largest businesses you believe should be interested and offer to build your product/service especially for them. This gives you a real world test site, honest feedback (you can tell if they have been using it or not) and, if they stay with you until the product/service is finished, a testimonial and reference site for future prospects.
Much more efficient than spending a year building a business only to find there is no market for it!