KaraK

Had my UK Turbo serviced on Friday, was told everything was fine then came to the car on Tuesday night to find it wouldn't start. Engine just wouldn't catch. Called out Subarau Assist. who managed to get the car started and t was accompanied by the reek of un-burnt petrol from the engine bay. Was told by the breakdown guy that the engine was running extremely rich and that I needed to get it checked out. Went by the dealership today who couldn't find anything wrong at all, no fault codes, no smell of petrol nothing. This is kind of worrying me to be honest, don't fancy this happening again and leaving me stranded.. again.

Any thoughts of what this could be?