>None of your solutions seem useful in this case, especially a $150 hold.

Attackers are going after small charges. That's the reason they're going after these guys in the first place.

>Site-wide rate limiting for payment processing? Too complicated, high-maintenance, and easy to mess up.

And then you give a solution that is 10x as complicated, high maintenance, and easy to mess up.

>You can't block 100% of these attempts, but you can block a large class of them by checking basic info for the attempted card changes like they all have different names and zip codes.

This is essentially a much more complex superset of rate limiting.

A $150 hold would clearly be noticed by the victim, so the attacker wouldn't even try it.

Maybe if my bank emailed me, otherwise I doubt it. Local gas stations routinely use $200 holds and I'd have to go way out of my way to see it happen.

The point is whether every user actually notices it, it's that enough of them do that attackers are specifically looking for the ability to do small charges. If you remove that capability, they will look elsewhere.

Yeah… no it wouldn’t. I’ve watched users have their bank accounts emptied (by accident) because they kept refreshing. A measly £150 isn’t going to register until it’s too late anyway.

There's a reason attackers exploit any site that lets them do small charges, it's because enough users will notice a larger charge.

Whether every user notices it or not, attackers are looking for the ability to do small charges, and if you remove that they'll move on.