Comment by nostrademons

If you have customers that are interested, and you end up burning the relationship, there are usually other customers that are interested. The real risk when founding a startup is that you end up building something nobody wants, because the need is made up. Once you have ~10 or so customers, you can be reasonably sure that there are more than 10 or so customers, because markets are almost never that small or that specialized.

(The exception is companies that are glorified consultancies, eg. you have just one customer that needs a very specific service done. But these are eliminated once you've triangulated enough to find 10 or so customers. At that point your product is general enough that it will no longer appeal to the companies that just want custom development outsourced.)