You unfortunately can't exclude specific companies from the search but you can exclude certain parameters (ex. industry, keywords) in the initial companies search to avoid any specific companies from being imported. Also, if you have a list of companies that you don't want in your table you could import the list onto clay and use Lookup Record to find matches between your "exclude these companies" table and working table to delete the matches.
And that’s correct about the find jobs from linkedin search — you can’t exclude industries there but if you’re finding jobs specifically at a list of companies (which you have in a companies table), you can exclude industries from that companies search
One of your colleagues credited around half of the credits back, not sure if that will be enough
Also, how can I exclude companies from the find jobs search? can you record something for me?