I need help. I sent a boat to a seller in the classified ads on a trade via UPS. UPS says it was delivered but he says that he didn't get it. Now he won't answer my emails. And UPS needs his phone number to further track the package but I get no response from him. This is the first time this has happened and I don't know what my next step should be.

When you listed and agreed to the trade, on your listing or his you probably sent an invoice. That invoice should have his #. If not, use his address and do a search through Switchboard, YellowPages or People Search online - or any of the other online search engines. If not perhaps an Admin can help.
Comickos