Referral checks allow you to establish block and trust lists of both good and bad attributes, affecting the risk score based on a known trend on many different shopper attributes.
We don't recommend using referral lists as strict block and trust lists. No shopper should be trusted, or blocked based on one list or rule. Rather these lists should affect the score, but work with other checks to either clear or block that transactions.
Note that all referral lists function at the company level. While a merchant must go to the merchant account level to change risk rules, all referral lists are aggregated at the company level, so any particular value only needs to be provided once to apply to all merchant accounts.