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Is it legal for a vendor to reuse credit details from a previous transaction
It is very much legal and in fact depending on the fine print of the purchase you make, you have now established a business relationship among which gives the business the right to hold on to your information (unless privacy policy states otherwise) and reuse it under certain circumstances (such as auto shipments) and when they called and asked you if you wanted it and you said OK, you acknowledged authorization. All legal even if pushy and less than pretty.