SCAM!
We found a flat through Geoexpat classifieds where the owner lived abroad. However, she got a friend to show us around and we spoke to the woman on the phone. We never handed over a cent until we got the keys and it was all fine.
Any situation where the whole thing is done via post though is an immediate red flag. If you don't have friends/family here who can help you a little then why wouldn't you use an agent? I know they are expensive, but so is your flat! I wouldn't want to rent my place out to somebody randomly over the internet by post.
Are you really asking this OP. Go to an agent. Trying to save a few bucks your gonna get scammed. Highly unlikely you would rent a direct owner flat online. And if it's good, it's already gone by the time it gets online.
Don't agree with this at all. Never met an agent here who does anything other than carry keys, they are a massive waste of money if you are the tenant and I would try to avoid using them wherever possible.
If you want to rent direct try the Geo classifieds, Asia Expat, Buy, Rent, Sell direct from owner. ZAP shows you how. - ZAP and if the area you are looking in has a local forum (such as DB or Sai Kung) also try that. If anybody suggests escrow or any other complicated arrangement, just walk away, it's almost certainly a scam.
Renting direct is perfectly do-able here, just takes a bit more legwork online.