BGA replacement using a high quality, fit-for-purpose rework station, by a trained operator in an ESD protected environment, is generally a very reliable operation. There's no reason why it shouldn't be.
The kind of 30-50% failure rates you're being quoted would apply to someone with a pair of tweezers and heat gun. There are a lot of people out there who claim to "know" how to rework a BGA, who don't follow anything even resembling a controlled process, but who nevertheless get away with it often enough that they don't understand why what they're doing is wrong.
The difference is between the service you'll get from a reputable contract electronics manufacturer vs a back street phone and games console repair outfit. There's a difference in price, of course. If you need the board to work afterwards, go to a good CEM. If you're on a budget, and just want to see if you can rescue some piece of consumer electronics from the bin, then the repair shop might be the only option that makes economic sense.