There is no scam in the topic as questioned by the original poster. If their is a scam it is by the guys seeking endorsements as a way to get free or discounted gear. You show your loyalty by your investment. If you want to project a great sound you will study the qualities of a great sound: how to develop it and what is the best equipment to deliver/embody it. You will then invest with your heart and then with your money. If you are wise you will have sought wise counsel on the material, brand, price point, and retailer or factory direct options for procuring the item. You will chose the company with the most viable and expansive range for your greatest chance of growth within the brand.
Seeking the endorsement is no different and in fact should be based on the above info and your personal experiences with the companies product if not also your personal interaction with their company owners/designers/reps/"A-list" endorsers. If you will not spend your money on the product why seek or except the endorsement opportunity. If you cannot see yourself encouraging your best friend, or greatest mentor to purchase/invest in the product line why except the endorsement? Does your word/integrity not mean something of value/quality? If a product does not represent your character... your voice well, then why should you represent it?
Building a brand as all companies have to do requires establishing a standard of integrity and sticking to it by proving consistency in delivery on time of ahead of schedule, constantly improving oneself, and empowering the consumer to sound better, look better, and grow better through experimentation and inspiration. In doing this the companies have to determine their target market and what that potential client's need are. This has to be done while allowing the company to grow make a profit that can promote further growth/product development. This requires consumer loyalty and quality consumers... decisive, conscious consumer whom invest in their future, their potential, their dreams/visions. This type of consumer realizes that the acheivement of their goals require constant evaluation, self-examination, and the building of a quality supportive team. Point being the endorsee (artist/musician/producer/studio/tour) and the company/vendor is team situation with mutual benefits. Compare it to NASCAR where the driver has to be able to car ad push himself and the car to the winners circle while nurturing a growing relationship with the car and the crew. This nurturing environment is then enable to respond in order to competition performance, techological growth, driver growth, fan/media feedback.
If you are a brand mixer check your loyalty card.
If your buy rather than invest check your quality card.
If you more about your look than your ingrity then check your personal value.
With all this in mind, be honest about your motives and what proven value you bring to what you do.
The best stewards get the best rewards... develop and guard your intgretity and unify with like-minded environments either as a dream builder or dream catcher and your name will be made great.