How to make sure the item is authentic?

[uk_ghasam]

I have bought trainers from “Japan” and I want to make sure they are genuine. 
how can eBay help me with that ? 

[plpmr]

when you receive your order, if they are fake open a not as described case.

[arkwebus]

eBay does not have that facility!  If you "think" they are fake that's all that matters!  Open the case for "not as described"  [not genuine]

The seller should send a label to post back to Japan.  They may claim that "they cannot".  EBay's advice a while back was to open the case and when the label does not arrive simply escalate after 4 days for a refund.

You may  have to pay duty and VAT on import.  If you  return you will have to try to get a refund.

@uk_ghasam