Endorsements are when a player is given discounted gear (as much as 100%) in return for services to the gear manufacturer. The bigger the profile of the performer the better the deal they are likely to be offered. The larger the company offering the endorsement the better the deal is likely to be.

If you have world wide reputation like Marcus Miller then it is quite likely that Fender will pay you handsomely for playing their gear and sticking your name on their basses, and even more handsomely to develop a signature SWR amp to tempt you away from your current EBS endorsement.

Likewise in the UK with Status King Bass and Ashdown MK amp.

Some high profile poo tubers with lots of friends have also been offered deals.