Credit card payments concerns

Hi,

Am after some advice really. I have been booking trips and hotels in Vietnam for April using all the fantastic advice from the people on this site.

Once thing I am a bit concerned about is paying by credit card. Almost every hotel and tour company we have contacted through advice from Tripadvisor users want us to send a photocopy of our passports and the front and back of my credit cards including Pilgrimage Village (Hue) and Columbus cruises (HaLong) to confirm our booking even though we have already given card details. I was wondering if this is normal practice. Has anyone else come across this? Is this usual practice?

Thanks