How can I find items by Specific Seller using Finding API?

To find items by Specific Seller, use findItemsByKeywords API : https://developer.ebay.com/devzone/finding/callref/finditemsbykeywords.html
Here is what you can do,

Use the Seller item filter (i.e., &itemFilter.name=Seller&itemFilter.value=seller1).

Limit is you can specify up to 100 sellers with this filter. You can retreive Items by Specified Sellers only.

Here's a sample call (wrapped for readability):


http://svcs.ebay.com/services/search/FindingService/v1?OPERATION-NAME=findItemsByKeywords

&SERVICE-VERSION=1.11.0
&SECURITY-APPNAME=YourAppID
&RESPONSE-DATA-FORMAT=XML
&REST-PAYLOAD
&keywords=Coby LED tv
&outputSelector=SellerInfo
&itemFilter.name=Seller
&itemFilter.value=inna_test