Project e-Sharing has developed an e-marketplace that supports the efficient sharing of resources among companies of the constructions sector (primarily) according to their time-varying needs. In this paper, we present the e-Sharing Trader system, which supports the leasing of resources by means of electronic auctions and negotiations. The Trader auction-related part supports a wide variety of single- and multi-object auctions together with innovative bidding agents for the English and the ascending clock auctions; these agents place bids on behalf of the users according to their specified preferences. The Trader negotiation-related part supports direct multi-attribute negotiations between users by means of a semi-structured negotiation protocol, automated agent-aided price negotiation, and two-object multi-attribute negotiations so that a user leases either two complementary resources or none, or exactly one out of two substitute resources. We also compare the e-Sharing Trader with existing e-marketplaces and discuss the advantages of our work.