And, please, let's get the terminology right. The company isn't looking to endorse the artists at all. YOU do the endorsing, not them. Understanding the verb is part and parcel of understanding what an endorsement deal entails. They don't help you out because they think you're great 'n' all. They want YOU to help them sell their stuff, and help them improve it.
So, look at it the way the correct usage of the verb "endorse" requires. From
Endorse - Definition and More from the Free Merriam-Webster Dictionary... Definition 2 b. "to recommend (as a product or service) usually for financial compensation <shoes endorsed by a pro basketball player>" So, when you approach a company about an endorsement, I think it'd be critical to understand what YOU bring to the table that would make it worth THEIR investment in you. You need to be able to "recommend" a product or service they provide. If you go in with the attitude that you're good so you should get free gear, then you don't seem to be doing the job. But if you go in and can show them:
A. You're already using their gear
B. You already are recommending it to other players.
C. You and your band have real, verifiable, and wide-spread influence on other players IN THAT COMPANY'S MARKET.
D. REALISTIC expectations of what they can provide you- a great regional band probably won't get free gear from a major manufacturer. However, they might get some help with promotions, get special service (e.g. you need an amp rig for a single TV appearance and you can't get yours delivered due to tight time constraints for other gigs, so the amp company you endorse provides one for you to use on the show), etc.
This is a case where I firmly believe that getting the semantics correct is vital to having the correct mind-set about the deal.
John