jasonloke13, i tik it's understandable to be afraid of having similar experience like ur frd did....honestly, u may or may not....it really depends on individual....
to ease ur fears, u may wish to speak to the neighbours who live in the same floor as the intended unit that u wish to buy and find out y the flat is now empty etc....another way, u can go to SLA and get the history of ownership for the intended flat also....
there is really no foolproof way of anything for this situation....to be honest, even if u buy a newly built flat, it can happen too...trust ur instincts...
if u feel tat u r being oversuperstitutious or wary, then try for HDB direct flat....like i said above, not foolproof either