Another who pays question

Had a major radio install on my Baron- a Garmin 530W and 430W. As part of
the install the avionics shop moved the radar display.

On the trip home (the same trip where in IMC the alternator quit) I turned
the radar on, since there were some storms over my home airport as indicated
by the nexrad.

Of course, the radar unit was completely dead. When I called the shop, they
said that they moved the unit, but that no one had checked its operation.

Now, I have to fly an hour each way to the avionics shop to fix the problem.

Who should pay for the gas? I realistically don't expect them to pay for two
hours of Baron flying time (which would probably negate any profit they made
on the installation).

However, is it unreasonable to expect them to pay for some of the gas?