I see no contradiction. It says that
you agree that you will not use this website or our services or
applications for chain letters, junk mail, "spamming" or commercial
solicitations or to send any message or Content that
[is clearly bad, as extensively described]
As a customer I can use the site to search for suppliers of bolts and request a quote, and as a bolt-supplier I can make my catalog of bolts available and can respond to requests for quotes. Nobody gets to use the website as a platform for launching commercial solicitations – spam, in one view of what span is. It's a business decision regarding how they will allow their platform to be used, and it is enforceable.