How Google Shopping Relevance Determined?

[BarrettAhern]

After looking at Google Shopping results, I was wondering how the "Relevance" is determined.  It would obviously be hugely beneficial to be ranked as one of the top 5 most relevant products, since that is the default sorting criteria.

Originally, I thought it was a combination of Price and Seller Rating.  But after examining a few examples, that doesn't seem to be the case.

When doing a search for "Radian XTSL" - a car seat that our website features - JustKidsStore.com appears at/near the bottom of the Google Shopping list, despite having a competitive price and ranking well for that term organically (8-13).

http://www.google.com/products/catalog?q=radian+xtsl&hl=en&safe=off&cid=15471698622239402479&os=sellers#

Do you know what the ranking factors are?  And if so, can you give a few pieces of advice for best practices?

Thanks!

[BlinkWeb]

Reviews, price and fresh data play a huge role.

This article is from 2009 but still very relevant IMHO.

http://www.seomoz.org/qa/view/7062/google-base-shopping-results