Contract = Offer & Acceptance (Payment of Deposit)
It's the old adage "buyer beware" or in this case "tenant beware" and shows the importance of using an agent and having all terms and conditions stated on a written contract.
Even though it's an online rental, the tenant can conduct their own due diligence e.g. only transfer deposit after contracts have been signed, checking online reviews, look at google maps for location, does the rental seem reasonable in comparison to what is on the market? If it's in line withe the surrounding areasm then the Judge could rule against you. At the end of the day, you get what you pay for...
Walk up apartments or "Tong Lau" are quite comonn in HK. Did the property listing state there were lifts?
If it were me, I'd look at something temporary like this. Different budgets to suit different needs:-
Nothing that you can do apart from go to court and pray the judge is on your side.