problem is they dont have a target light on them to they... so no hope of checking them for wow and flutter.
and they are numark, wouldnt EVER bother with numark/korg DJ equipment i have Cig Packets which have better construction.

Sell em on thats my advice.

if you do want to check them, get a record with a constant tone on it and listen for fluctuations.

or set both decks at quartz lock and get two copies of the same record and sync them up and see what happens.