One thing i've done prior to letting someone view is take a small payment through pay pal which has a verified address. This can be refunded after the viewing or taken off the sale price. It doesnt need to be an ebay transaction to do this but people new to paypal wont be verified so it wont work in every instance but definitely through ebay as the buyers will be aware of paypal.
It also helps if buying to pay a deposit through paypal, as if something turns out to be really rotten with the bike, paypal will automatically hold your deposit until the buyer and seller agree an outcome, i had an instance where i bought an Evo and didn't spot the cracked swing arm, whilst cleaning and greasing the bike i found it was not only crack but repaired multiple times and the buyer should definitely pointed it out, Paypal held the funds so the seller had no choice but to do a deal.
Luckily though the renowned and wonderful Beta customer service gave me an exchange for a brand new swing arm.