If the bike was hours away I could kind of understand asking for a deposit but I'd sure as hell want to make sure the person is real before just sending money into the ether - get the guys phone numbers (home and cell), email addresses (his real one, not the Kijiji email relay address), his physical address, and then physically call and talk to the seller.
If they're evasive on any of the above, run away - it's probably a scam.
That said, unless you're asking him to hold it for you for several days....go and physically see the bike, bring the deposit, and if you like what you see take photos and get a piece of paper confirming the receipt.
If he's too impatient to even hold the bike for you for a few hours without a deposit, well, personally, I'd move on.