The first step is to know the trouble code. What code did the local dealer find?
Ultimately, however, there is probably no way for someone over the internet to do a better diagnosis than the dealer that actually inspected the vehicle. If you don't think they're correct, or if you'd just like some insurance that the diagnosis is correct, your best bet is probably to just go get a second opinion at a shop qualified to do diagnostics on ABS systems. Don't know what country you're in or what chains are there, but in the U.S., the run of the mill brake chain shops would be a very poor place to have this sort of diagnosis done.