OK, I'll chime in a bit, since I have a pretty good perspective on the topic (AR [Artist Relations] is one of the several hats I wear at work):
Remember, any relationship is a two way street. You have to have something concrete to offer a manufacturer to enter into an artist/endorser relationship - mainly, you get consideration (rarely FREE stuff) on pricing for providing excellent visibility for a product that you believe in.
Being in a really good local cover band: not getting a deal.
Being in your local church band: not getting a deal.
Having the chops of doom, but no regular, highly exposed gig: not getting a deal.
Even an average to maybe not even average player that is in a band that a LOT (250 drunks at the local pub on Friday and Saturday night is NOT a "lot" of people - 500 people on 6 out of 7 nights a week in various small venues on tour, starts to add up to a lot of people, especially if it is a several months long tour) of people see on a regular basis can get you a deal.
Being a very well known and respected musician (say...Jimmy Haslip

) will open doors.
The bottom line is that the more visible you are, for whatever reason, the more likely any manufacturer will be willing to work with you. Without something to offer in return, the manufacturer has zero incentive to do anything at all, and can't do anything, as the instrument costs them money to make, and we all - both players and manufacturers - are not charity organizations.
Keep in mind that the builder/manufacturer has overhead (rent/mortgage, business loan payments, payroll, materials costs, taxes, utilities) that needs to be serviced, and not selling an instrument at the standard dealer pricing COSTS us money, thus affecting our ability to operate at a profit (much less break even, which trust me, most of us struggle to do more than break even!). You, the artist, must provide some return on capital investment to justify any consideration at all.
Hope that helps to give a full perspective.