When choosing to buy a BGA rework station there are many factors to consider.
The most common factor considered is pricing. Doing a search for completed items on ebay you can find the T862, T870 and IR6000 being sold the most. These are the cheapest actual BGA stations you can buy. Some will actually purchase an IR preheater T8280 and the Aoyue 968 SMD station, there are definitely not meant for BGA reworking due to the lack of power. Most rework stations for BGA are around 2000 watts. Due to the cheap cost these machines are sold very often and the users tend to complain about rework success.
The quality is usually in direct correlation with the price. These cheaper models most always use cheap components and the internal wiring is not done safely. Ceramic heaters provide uneven heating, SSRs are made in China and do not last. Wires have improper crimps which may come loose over time.
Warranty is an overlooked factor but is quite important. Would you buy a car with no warranty or support, do you know how to fix it yourself if something happens to it? Well most BGA rework machine manufacturers expect that from you. After purchase of a machine, if it arrives with damaged heaters they will ship you replacements that you have to install. Did they forget to include an important accessory or did your relay blow, they will agree to take care of you but they will ship those parts out via Air Mail. Now didnt you get the rework station via Fedex or DHL? Why should you have to wait for parts to be sent out just so they can save some money on shipping?