I hope this is not OT, but, if you want technicalities I can supply them. I worked on the design of custom "referral" logic for some major issuers/sponsors of credit and charge cards. NDA's preclude names, but the generalities are public, if not widely known. Basically there are three levels of approvals for credit card transactions:
1) Floor limits- allow approval based, in automated systems, on verification of card good status;
2) automated verification- beyond verification of card status, provides automated verification that the card issuer accepts the authorization;
3) Referral to issuer. This commonly results in a few oral questions to the cardholder posed by the issuer call center. Large issuers have specific policies which normally are held very closely. These policies are often not even internally known outside the groups that administer them. This category includes cards that are coded for specific exceptional processing when a transaction is referred to the issuer. Candidly there is no such thing as a card that is never declined. However, for extremely high value customers there are customized rules that are applied, almost all of which use some form of positive verification. These rules include pre-authoization for specific transactions (i.e." I will be buying a Tesla P100D at a purchase price of $151,000 plus taxes. The seller will be Tesla Motors, Inc and the transaction will be sometime later today ("this must make the Tesla quarterly sales report, right?). The issuer account representative will note the transaction in the account, so when the transaction as described comes through the automated referral system it may be approved without actually appearing to have anything special. if the seller turns out to be, say Ferrari of Newport Beach the transaction will not be declined but there will be a lengthy series of verification questions which, for most issuer, will include a description of the original authorization request.
The third step for ultra-large transactions only exists for a handful of issuers worldwide. It is uncommon. Smaller issuers rarely have actual card limits and policies designed to do such things.
For anybody who desperately wants more detail, PM me. I cannot give anything propriety but I can refer people to sources for processing rules. However, at a bare minimum people need to understand SQL to read even the user-level rules, and the ones that are publicly available are general 'one-up' rules that can apply in card processing systems.