If it has the Premium Pkg., it would have had a TCU in the rear cargo area driver side, behind a panel.
2008 X3 3.0si Premium Pkg.
Leather upholstery, front-seat lumbar adjustment, BMW Assist system w/one year service, wireless cell phone link, automatic day/night rearview and outside mirrors, compass, universal garage door opener, additional interior lights.
Previous owner may have removed it because it was faulty (sometime known to go into a loop and drain the battery).
Or the selling dealer yanked it out to sell on ebay?
In earlier model years, TCU and ULF were different boxes, but became integrated into one box.
Bluetooth compatible sounds a bit weaker than Bluetooth enabled to me.
You may or may not have a case based on semantics for the seller to pay the cost of a TCU.