Im after a new set of standard vrs wheels for my fabia because a a couple are buckled, dam pot holes! How can I tell when buying second hand that none of the replacement ones are already buckled?

Stick them on a wheel balancer and watch them.

Or if you have two of the same rim without tyres put one on top of the other and wobble the top one to see if any play. Its a not full proof but its a good indicator.

No wheel balancer available if buying them second hand from someone's house

Im after a new set of standard vrs wheels for my fabia because a a couple are buckled, dam pot holes! How can I tell when buying second hand that none of the replacement ones are already buckled?

You need to have a careful look at them. Though look carefully at any advert before travelling...

Look around both inside and outside rims/beads for any deviation in either plane (wobbles/bends/dinks). With VRS alloys, also check the backs of the webs behind each wheel spoke for signs of cracking.