本句是简单句，主谓宾宾补结构。

句子主干 accounts made the idea irresistible。

Widely reported是过去分词短语作状语, if somewhat distrusted,是带连词的过去分词短语作状语 accounts是主语 by figures like the famous traveler from Venice, Marco Polo, of the willingness of people in China to trade with Europeans and of the immensity of the wealth to be gained by such contact是定语 made 是谓语the idea 是宾语irresistible.是宾补

句子意思：很多人,如威尼斯著名旅行家马可波罗,对中国人愿意与欧洲人经商以及这样的合同将要带来的巨大财富的记述,（如果说还有些令人将信将疑,但确已广泛报道,）使得这种想法难以抗拒.