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Mark, Antje and Bley, Sabine and Helm, Roland (2009) The effect of free product premiums on attitudes and buying intention for durable goods: moderating effects of value and product premium fit in the dual mediation model. European retail research 23 (1), pp. 21-45.
Helm, Roland and Mark, Antje and Bley, Sabine (2007) Kleine Absatzförderer. www.science-factory.de 9 (3), pp. 7-9.