First off welcome to the BMW X5 Family.

Unfortunately the air suspension on the X5s do tend to have issues around the millage you have. But don't worry, Most us who did have that issue got through it and past it and in the near future I am sure you will as well.

Normally its the 4.8i versions of the X5s that have air suspension in the front and the back, the suspension air bags must have leaked and I honestly do not believe its due to the shop you went to. It seems to me that a very rare few 4.4i's have air suspension in the front, I have a friend of mine who has it but he had it done himself. To make a long story short, go to any local mom and pop shop and tell them the situation. Ask them to call up their local BMW parts & ask them how much would it cost for the air bags, then see the price he/she gives you, match it with realoem.com or another source you get and see how much it would cost to replace.

Good luck!