If you don't want to see a particular seller's items in your search results, you can block them from showing up.

IF YOU HAVEN'T DONE THE SEARCH YET:  Click on the Advanced Search link in the upper right-hand corner of any eBay page.  If you get a short page of search options, click on the Advanced search link at the bottom of the page.

Enter the words you want to search, then scroll down to the From Sellers section.  The part you need looks roughly like this:

O From specific sellers (enter sellers' user IDs)
    [ include ][v] [__________________________]

Tick the box in front of the line that says: "From specific sellers (enter sellers' user IDs)".  In the line below it, click the down-arrow and choose "Exclude."  Then enter the seller's user ID - in fact, you can enter up to 10 of them (in eBay's new search, you can exclude many more than 10).  When you've done that, hit the Enter key on your keyboard and your search will be performed.

IF YOU HAVE ALREADY DONE THE SEARCH:   If you have already performed a search and find it ... ahem ... cluttered with too many listings from one or more sellers, you can filter out those listings quickly. Take note of the user IDs you want to exclude, then click on the tiny Advanced Search link above the first listing on the yellow bar. Scroll down to the From Sellers section. Tick the box in front of the line that says: "From specific sellers (enter sellers' user IDs)". In the line below it, click the down-arrow and choose "Exclude."  Then enter the user IDs you want to exclude. Lastly, hit the Enter key on your keyboard and your search will be performed.

IF YOU ARE BROWSING THE LISTINGS:  If you clicked on the Buy button then navigated to a list of items in a subcategory, you can remove sellers' listings as well.  Click on the tiny Advanced Search link above the first listing on the yellow bar. Leave the search box blank, then scroll down to the From Sellers section. Tick the box in front of the line that says: "From specific sellers (enter sellers' user IDs)".  In the line below it, click the down-arrow and choose "Exclude." Then enter the user IDs you want to exclude. Lastly, hit the Enter key on your keyboard and your search will be performed.

Note that at present there is no way to permanently exclude seller's listings; the above must be done each time.  eBay administration sees no need for a seller block function (yet).