[UKCardGuy]

Another way to assess the potential current value is to use other comparable cards from the same set. If there are other similarly hard to find cards from the same set then you have data from those salws too.

I tend to compare the sales history of similar cards and then make an adjustment foe geneeal cards price changes since those sales.

Its not perfect and It doesn't completely solve your problem because the seller might not agree with your logic. But for me it helps me to assess what i think a fair price is.