Some things that can help.... Keyword in the product title, keywords in the product description, keyword in the image name/title text, low price, use Google Checkout, update your feeds daily, etc.
Google seems to have a different set of criteria for ranking in the product search. Some of ours will be in the top 3 for a week or 2 then go back down. It has been this way for a long time now.
check the keywords in the title,description. Offer low prices and keep your feeds updated. Thats what many people would recommend
Its a completley different alg. I have done a bit of research into this in the past few weeks and noticed that its about not being too spammy, whereas in your meta descrip you can use the keywords 4/5 times, Base prefers you to use your keywords only once/twice dependant on how long your title & description is. There is a bit more to it but it is late and i cba'd Using google checkout is absoloute bull though.. From what i have been doing in the last few days for my products i am out ranking most of the competition for the same products and that includes people with "Ratings" & people using google base. The traffic is good from base but the conversion rate is shocking considering i am using pretty long tail keywords.