I haven't come up against anything like having my card blocked based on what I was purchasing as of yet ( i.e. firearms) I have however had my card cut off as sort of a pre-emptive security measure. When I was last buying a new computer, all in components, they put a halt on my card until they could contact me and verify that the myriad expensive purchases in the same day and from varied locations were actually made by me. It was very annoying when I went to pay for a meal and got denied.. but on the other hand it's good they they were looking out.. sort of.