TheFind is a comparison shopping search engine that is unusually clean — it doesn’t ask merchants to pay for their products to show up in results. TheFind’s traffic is growing.

This purity is one reason it has just won $15 million in fresh backing from big-name investors Bain Capital, Redpoint Ventures and Lightspeed Venture Partners.

The investment, to be announced tomorrow (Thursday) makes TheFind one of the best-funded of the new shopping search engines. It wants to do to shopping what Google did to general search seven years ago — turn it upside-down by making results as relevant as possible to the user. Search for “Victoria Secret” for example, and TheFind will return plenty of results listing clothing made by that company. If you do that at Shopping.com, you’ll get nothing, because Victoria Secret refuses to pay it.

Shopping.com and a wave of other early players have matured and seen financial success — and yet all of them demand payment from retailers in return for showing their wares. With so many players, you’d think the game would be over: Nextag, Pricegrabber and Shopzilla.com — all are huge. Most recently, Nextag recently received a major investment that valued it at $1.2 billion. A slew of other start-ups, from Retrevo to Become.com, have launched too — but none of the smaller players have gotten major traction. None have received major amounts of funding.

Thefind seeks to crawl as much of the Web as possible to search for hard goods (electronics, cameras, etc) as well as soft goods (furniture, clothing, etc).

We should note that after our initial favorable review of TheFind back in March, we made several qualifications a week later when we came to realize that TheFind was not as pure as were initially led to believe. These were largely temporary issues. At the time, TheFind’s sponsored ads at the top of returned results were not clearly marked as such. TheFind has since marked its sponsored results clearly as “sponsored”. In addition, TheFind was paying for ads at search engines to attract traffic to its site, in an effort to market itself. So while it boasted a million unique users, we discovered that half of those users were directed there by an ad (suggesting its growth wasn’t as self-fueled as we’d believed). However, TheFind has since reduced its payments for such traffic. This month, 80 percent of its two million unique monthly users this month are be people going directly to the site, said chief executive Siva Kumar.

TheFind.com says it indexes 170 million products and 500,000 stores.