Personally I think they're trying it on, so assuming you were given some sort of paperwork in relation to the garage warranty then I'd suggest you have a good read through it - including any terms and conditions. Unless it specifically states that the cost of diagnosis is borne by the vehicle owner then tell them to go swivel. 
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This vehicle was born on Wednesday June 4th 2003 @ 08:24:38
This vehicle was the 73,905th 75 to run off the production line, out of 112,381
This vehicle was the 1,862nd 75 1.8 T Club SE to be made out of 3,980
This vehicle was the 6,856th 75 in Wedgewood Blue to be made out of 7,515 Wedgewood Blue 75s
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