There is a EN certification (CEN12491) for parachutes now that tests the descent rate and the opening shock load capability of the design. DHV also certify parachutes but to a higher descent rate. There is no longer any reason to buy a parachute that is not certified and whose descent rate is not known and tested. There is also a move towards a pan European parachute packer licence to qualify and standardise the re-packing of reserves and their fitting to harnesses. Currently the BHPA EPPL (emergency parachute packer licence) is the proposed model for the European licence.
EPPL holders can be found here http://www.bhpa.co.uk/members/safety/packers/index.php
When buying a reserve second hand you need to know that the certified all up weight of a canopy is the the max weight it should carry to give a particular descent rate. (don’t just take the placarded AUW at face value). If the canopy is DHV certified the descent rate is 6.8m/s which can result in injury. The DHV now recommend that you take 75% of the AUW stated on a DHV certified reserve as the max AUW and NOT the placarded AUW.
EN certified reserves are certified AUW for 5.5m/s descent so 100% of EN certified AUW can be applied. (see safety advisory notice http://www.bhpa.co.uk/pdf/safety_advisory/sa008.231205.pdf )
The descent rate is the important number and is not directly related to size. If it has no certification you have no way of knowing what descent rate you can expect, or what opening load it will take or if it will remain stable or swing about wildly, whatever the seller tells you.
Steerable reserves have extra complications.
When buying any second hand emergency parachute ask yourself, "why is this person getting rid of this reserve"? It is more than 10 years old? Is it uncertified? Is it a "steerable"? Is the descent rate 5m/s at the AUW I will be using it with. If it is a serviceable, certified reserve why are they not keeping it?
The BHPA club organised repacks are often under-subscribed and open to non BHPA members. There are many, many BHPA paragliding and hang gliding clubs where these repacks are happening. Learning about your own reserve including lectures on deployment and harness fitting is a valuable experience