Ask HN: How to validate my B2B SAAS idea

I'm trying to work out how I can validate my B2B SAAS idea. I have a solution to a specific 'pain' that certain business's have.

I've already done a custom version of the program for a specific company - and they love it. But I want to make it more generic and market it as a SAAS.

I've made a landing page similar to the twitter Buffer App idea - but the problem is I'm only getting 1-2 users a day after a month because I rank poorly on the SEO for the search terms.

I was thinking of using google ad words - but I thought it might seem silly advertising a product I dont yet have?