Yes, you can research your competitor by eBay seller id, but we only show a portion of their listings and their sales. We understand the importance of benchmarking yourself against your competitors so we present up to their top 500 listings. You can create report queries that use both eBay ID and keywords and/or categories so that you can get a more focused set of top 500 listings.
When searching for a specific seller, use their eBay Seller ID, not their store name. Be sure the country selected is a market that the seller is active in otherwise it will return zero listings.