worst case from what i hear is customs give your local police a call and they go to the address it was getting shipped to. i saw a news story about a guy getting seeds sent to his home where he was growing outdoors and when police showed up ...well u get it. His next decade of life prolly is goin to suck hardcore(he was growing hundreds of plants)....i would say that covers worst case possible.
i sent cash once...that worked out good and used my card once also. If the seed bank has their shit together and is willing to destroy your card info upon request IMO thats best.