The relevant requirements in the VIOR are:

https://usa.visa.com/download/mercha...n.pdf#page=530

"- Cardholder expressly agrees to DCC by marking an "accept" box on the written agreement"

The trouble is merchants don't even require a signature. Consider the two following cases:

- Shenzhen - Mastercard presented for deposit, nothing in check-in slip nor booking engine suggested DCC, told hotel will simply post the deposit on checkout, only found out about DCC when deposit post refused and a seperate charge is signed

- Amsterdam - Non-cancellable hotel rate charged on check-in, nothing mentioned about DCC until statement review in HK

In the second case (and the first case if express checkout agreed to) there is nothing for the cardholder to stamp - the card info was submitted online and the booking was all done online.

This is an especially nasty problem in jurisdictions like Hong Kong and Singapore where (in violation of the VIOR) banks do not do anything until you present a prima facie case to force them to.