I frequently saw rates between 5.25% and 5.45% on slips where I successfully rejected DCC during my recent trip. Always written in very small text as FIVE PT. FOUR FIVE PERCENT, presumably because figures would too likely to jump out.

I just had a 98,275 KRW charge post to my Visa card as 82.07 USD. The DCC charge that I rejected would have been 87.25 USD. That would have been a stonking 6.31% premium. Hotels (this was a Hyatt) seem to be the greediest of all.