++++ Tax provisions - Harmonization of laws - Turnover tax - Common system of value added tax - Taxable amount - Supply of goods - Consideration may consist in a provision of services - Condition - Provision of services directly linked to the supply and capable of expression in monetary terms - Supply of an article without extra charge to persons introducing themselves or other persons as new customers - Purchase price for the supplier of the article supplied (Council Directive 77/388, Art. 11A(1)(a))