I posted this a Arranger forum but I'll edit and repeat:
IMO because you have no feedback and because of all the scams involving keyboards you're gonna have a tough time.
You used paypal?
Do you have a friend or relative that has an ebay acct with positive feedback.Do you write a personal description of the item or just copy the Yamaha info? People who look already know the specs or can look them up on line you have to sell yourself as a first time seller.
Do you run actual pictures of the item?
If you have a studio set the board in the studio so people can see you have other instruments. Not close ups just a general background thing.
I would put in a note that bidders may contact you by phone. I wouldn't include my number but if anyone is interested enough to email you give them the number you have to establish trust. That is also why I would write a little about yourself and why you're selling. I may try a little humor "I have two and the wife says me or one of the boards is gotta go". Personalize your listing tell them it's your first time selling on ebay, tell them a little about yourself. If you play gigs in your area tell them you are a working pro. But again only tell them where if they call you
Look into an escrow service they hold the money until all parties are satisfied. I've never used one but by the time I got around to selling a big ticket item I already had a good feedback and track record. See if eBay recommends one and make sure it is one of your choosing if you go that way.
http://pages.ebay.com/help/tp/payment-escrow.html I think the trust issue is you're biggest downfall thats a big item for a guy with no track record.
At least those are some of the things I look for when both buying and selling.