A trust score is the rating The Campaign Registry assigns to a registered brand after it is checked against public business records and, optionally, vetted by a third party. The US carriers read that score to decide how many messages a day, or a minute, the brand's 10DLC campaigns may send, and how aggressively to filter them. A higher score means more throughput and better deliverability.
How the score is set
Brand registration on its own produces a basic score from the match between the legal name, EIN, address and website you file and the public record. A mismatch, a trading name in place of the registered name, or a website that does not identify the business, all pull the score down. Optional vetting by an approved provider, listed at $41.50 for standard and $101.50 for enhanced on the SimplyRCS rate card, reviews the business in more depth and typically raises the score. Political and charity campaigns have their own vetting paths.
What it changes
Carriers map the score to throughput tiers. A well-vetted brand on a standard campaign may send an order of magnitude more traffic per day than an unvetted one on the same number, which is why vetting is a deliverability decision rather than an administrative one. The score is per brand; every campaign under it inherits the tier.
On SimplyRCS
Registration and vetting are prepared and filed for you, with the option to vet explained before you pay for it. How 10DLC registration works covers the steps.