usually a person can resell a 5/8 german swirl between $7-10 each. if you can buy them in the original box for $600-700, or less, id say buy em, if their mint of course.
my old neighbor brought a jar of his marbles outside for us to play. in this jar was a black base white line clambroth. and a white base, pink and blue line clambroth. needless to say, we dpdnt play with those,....................i bought em