Purchase of plot from original allottee in islamabad g sector

Sometime the housing societies have files with them from the original allotees who are not able to pay the charges and have not transferred to plots by paying society charges. If we go to buy that property, what are the prons and cons (plus or negatives) and is it safe to purchase such property. The agents are asking that it will take 4 months to transfer the plot first to original allotte and then to your name. Can the allotte transfer the plot immetiately to my name or is there any minimum time. You will not know the plot number and only islamabad sector will be known to you. The plot number will be alloted after transfer. Please give suggestion.