(69)Centralised purchasing techniques are increasingly used in most Member States. Central purchasing bodies are responsible for making acquisitions, managing dynamic purchasing systems or awarding public contracts/framework agreements for other contracting authorities, with or without remuneration. The contracting authorities for whom a framework agreement is concluded should be able to use it for individual or repetitive purchases. In view of the large volumes purchased, such techniques may help increase competition and should help to professionalise public purchasing. Provision should therefore be made for a Union definition of central purchasing bodies dedicated to contracting authorities and it should be clarified that central purchasing bodies operate in two different manners. Firstly, they should be able to act as wholesalers by buying, stocking and reselling or, secondly, they should be able to act as intermediaries by awarding contracts, operating dynamic purchasing systems or concluding framework agreements to be used by contracting authorities. Such an intermediary role might in some cases be carried out by conducting the relevant award procedures autonomously, without detailed instructions from the contracting authorities concerned; in other cases, by conducting the relevant award procedures under the instructions of the contracting authorities concerned, on their behalf and for their account. Furthermore, rules should be laid down for allocating responsibility for the observance of the obligations pursuant to this Directive, as between the central purchasing body and the contracting authorities procuring from or through it. Where the central purchasing body has sole responsibility for the conduct of the procurement procedures, it should also be solely and directly responsible for the legality of the procedures. Where a contracting authority conducts certain parts of the procedure, for instance the reopening of competition under a framework agreement or the award of individual contracts based on a dynamic purchasing system, it should continue to be responsible for the stages it conducts.