In the fine print, eBay specifies that it is not liable for non-payment or non-delivery regarding transactions between seller and buyer. It offers a service to connect buyer and seller, and considers itself to only be a "advertiser", such as a local newspaper company, and not a party to the actual transaction. You wouldn't sue The New York Times for publishing an ad it placed in its newspaper which resulted in a negative transaction; you'd sue the party who defaulted on the sale. What eBay does offer in this regard is: 1) insurance to cover your purchase (for an additional fee through non-affiliates); 2) negative points and comments advertised against the wrongdoer, which are publically displayed on eBay's website; 3) banning the registered member for inappropriate and/or fraudulent behavior.
As to your current situation, did you purchase the insurance offered by eBay? If not, what form of payment did you use to purchase the motorcycle from the seller (PayPal, money order, check, credit card, cash)? We would need to know your answers to these questions before we can make any further suggestions in helping you.
