Complex sentence: European farmers were given a "guaranteed" price for their produce when it waa sold in the European Community, and a system of export reimbursements ensured that European exports would sell at or below world prices, at no detriment to the European producer.
Split into simpler sentences: European farmers were this given a "guaranteed" price for their produce when sold in the European community. In addition, a system of export reimbursements ensured that European exports would sell at or below world prices, at no detriment to the European producer.