There are seveal eBay sellers ofering numerous Canon "L" series lenses at unbelievable prices with no shipping or payment methods posted.  When you contact them via eBay and ask them questions about shipping and payment, they respond to your email and begin correspondence outside of eBay.

They insist for various reasons (some are pretty amusing and implausible) that you proceed with the purchase outside of eBay.  They claim that the transaction will be conducted through an eBay representative, but not through the eBay auction process.

I believe that transactions that take place outside of eBay are not eligible for any eBay or PayPal protective services and you could rund the risk of losing your money or the item you purchase.