If you have the original tittle certificate of the seller, verry little can go wrong.
Normaly a tittle transfer will take 3 months upwarts, i know a real estate brooker in Cebu who does it in 2 weeks.
BIR is no problem, in fact during the whole process you receive a date when you may pick up your papers EXEPT from Registry of deeds.
So if time is an issue R.o.d. will need some grease and that is the only place in the whole process.
Most critical points where it may go wrong:
Original tittle of seller "lost"
Owner of the tittle deceased and child(ren) dealing with the interested buyer.
Real estate tax for many years not paid,
Bad homework and negligence.
Lack of funds to pay for Capital Gains Tax, even it is the seller who has to pay for, how can you force someone to pay ones the money is already gone.
And of cause the ever returning capital word TRUST.