We've found that the best way to validate here without getting caught out by people who aren't really prepared to pay for your product is to build a spoofed marketing site.

This might feel like a slightly misleading technique. But in our opinion, as long as you're not actually taking people's money for something you won't deliver, users will be understanding of your motives.

It's a very common technique because it works so well. Let's take CheckMaid.com for example. It's an online service for finding and booking home cleaning services. But when they first created their website, there wasn't a real business behind it. As founder Alex Brola said:

"We actually validated [the idea] without having any cleaners to do the cleanings. We threw up a site, a booking form, a phone number, and ran some [pay-per-click] ads through Google and Bing, and saw what the conversion rate would be had we actually had cleaners."

Tailwind (a Pinterest analytics tool) used a similar technique to try and make sure that people other than their friends and family would sign up:

"We 'validated' our first (failed) product by having friends and family tell us how wonderful it was. [It] felt great, but they didn't use it. When we started Tailwind, we took a different approach -- asking complete strangers who didn't care about us at all to [sign up] and pay before our product was even built. We created a sign up page, bought some AdWords traffic and people actually started offering to pay us! We didn't actually charge them, but we learned we were onto something."

Validating willingness to pay using a spoof landing page is definitely something you need to be careful about. If you do it wrong, you could damage your brand and create a huge amount of user frustration. The key is to present your marketing content and display a visible "Sign up" or "Buy now" link. When the user clicks the link, you would display a message explaining why the service is not yet running, and offer them the option to enter their email address to receive updates when you do launch. Also, a good idea would be to reward these early users by saying they're entitled to discounts or other rewards for being early supporters. We'd recommend not going any further than storing the user's email address (so that you can contact them later) and possibly their general location if that's relevant to your product (to gauge regional demand). Make them aware as early as possible in the process that the product is not available. Many laws, especially in Europe, prohibit misleading advertising - be very careful not to take payment or sensitive personal details in a misleading way. If you'd prefer to avoid a spoof landing page, you could opt for the concierge route, which is less ethically sensitive and often a good alternative.