lets say im selling dog food.

when i search "dog food" [Best Match option] in ebay, how does it choose what order to list the items in?

does it have any SEO techniques it follows? or is it simply based on seller scores, or what?

I believe it goes by the account standings. I noticed If you have a lot of positive feedback, you are more likely to be listed higher

It goes by:
-account standing ( Top-Rated Seller or NOT )
-Your product title
-The number of times it sold in the same listing
-Views/per conversion
-Watchers
-Desirability
-Feedback received
-Performance

Choosing right type of titles is important, you should see the listings that appear on top of search results and then try to pick out the differences between your listing and the one much above yours. Then you will know exactly why some sellers who are not 'Top-Rated' appear on page 1.

eBay basically wants to get those listings on top that are likely to get sold or is selling already and wants to push down the listings that are perform-ing poorly or not getting sold. Clearly, as all businesses, eBay has their motive. If something sells on eBay. They will benefit aswell as the seller. Therefore, make sure you are benefitting eBay in return you will be benefitted.

I have always noticed, when I keep a high quantity on my listing and it is selling constantly. It will jump on top of other listings, but when days pass and no one has bought on my listing, it will come tumbling down. After some extensive research, this is what I have concluded:
-Don't let your Fixed-Price listings end at any cost. ( keep feeding it quantity ).
-Keep good tiles, include only keywords which buyers use to search and exclude the words that are never used for a search.
-Include good number of pictures in your description through the HTML function.
-Open up a store to benefit from 12-free pictures and lower listing fee.
-Mention the features, because some buyers search your listings with features. ( features in the seperate option )
-Have a strong refund policy ( I have 60-days! )

If you do everything right, it is more than likely you will stand higher than your competitors on search.

I'll appreciate any further input into this.

Thanks