Greystone's function is to report payment history to credit bureaus, not to provide quality jewelry. Their prices are a literal 10 times those at standard retail establishments, their selection is poor, and the quality of their merchandise is mediocre at best.
Greystone extends credit to all applicants. They will interview you first about what you believe to be on your credit file, pull a credit report, review it with you in the event of discrepancies, and assess your creditworthiness. In addition to your credit report, your credit limit will be based heavily on your job, length of employment, and time living in the area. If your credit is painfully bad, a down payment will be required (that will likely cover the wholesale cost of your purchase, as the markup here is steep), but you will still be granted a line of credit and encouraged to spend the max. They will attempt to sell you up to your limit, regardless of your creditworthiness.
Greystone requires a list of personal references at the time credit applications are submitted, and they will call these references and recruit them to find you and let you know that your account is past due if your payments lag.
Again, Greystone's primary offering is credit reestablishment, not spectacular jewelry. They will, indeed, report your payment history religiously to the credit bureaus they claim, and will discount prices to long-time/good customers or customers with better credit histories. Their services may be worth the price if buyers are honest with themselves about the services they are seeking; this is a valid means of establishing good payment history and creditworthiness for those in need of help.